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Woods  Hole  Oceanograpiiic 



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IS.  Department  of  the  Interior 



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Woods  Mole  Oceanographic 


This  is  one  of  the  first  reports  to  be  published  in  the  new  "Biological 
Report"  series.  This  technical  report  series,  published  by  the  Research 
and  Development  branch  of  the  U.S.  Fish  and  Wildlife  Service,  replaces 
the  "FWS/OBS"  series  published  from  1976  to  September  1984.  The  Biolog- 
ical Report  series  is  designed  for  the  rapid  publication  of  reports  with 
an  application  orientation,  and  it  continues  the  focus  of  the  FWS/OBS 
series  on  resource  management  issues  and  fish  and  wildlife  needs. 

Biological  Report  85(7.2) 
May  1985 



Michael  S.  Foster 


David  R.  Schiel 

Moss  Landing  Marine  Laboratories 

P.O.  Box  450 

Moss  Landing,  CA  95039-0450 

Project  Officer 

Wiley  M.  Kitchens 

National  Coastal  Ecosystems  Team 

U.S.  Fish  and  Wildlife  Service 

1010  Gause  Boulevard 

Slidell,  LA  70458 

Prepared  for 

National  Coastal  Ecosystems  Team 
Division  of  Biological  Services 

Research  and  Development 

U.S.  Fish  and  Wildlife  Service 

NASA-SI i del  1  Computer  Complex 

1010  Gause  Boulevard 

Slidell,  LA  70458 


The  nention    of   trade   names   does  not  constitute  endorsement  or  recommendation   for 
use   by  the  Federal    Government. 

Library  of  Congress  No.   84-60117. 

This  report  should  be  cited  as: 

Foster,  M.S.,  and  D.R.  Schiel.  1985.  The  ecology  of  giant  kelp  forests  in 
California:  a  community  profile.  U.S.  Fish  Wildl.  Serv.  Biol.  Rep.  85(7.2). 
152  pp. 


Submarine  forests  of  giant  kelp 
(Macrocystis) ,  with  plants  over  50  m  tall 
growing  from  the  bottom  to  the  surface  of 
the  sea,  probably  intrigued  humans  long 
before  the  first  published  insights  into 
their  ecology  by  Darwin  in  1860.  Even 
with  only  a  limited  view  from  the  surface 
and  observations  from  collections,  Darwin 
was  clearly  fascinated  by  giant  kelp  and 
the  diverse  organisms  associated  with  it, 
and  made  the  first  analogy  between  this 
community  and  terrestrial  forests.  Except 
for  a  few  subsequent  reports  on  the  extent 
of  the  Macrocystis  resource  in  California, 
it  was  almost  a  hundred  years  after 
observations  in  South  America 
study  of  California  kelp  forests 
Andrews'  (1945) 
on  the  fauna  of 
included   some 

that  the 


giant  kelp 


observations,  but  this  and  other  early 
studies  were  hampered  by  the  lack  of 
simple  diving  equipment.  With  the  advent 
of  SCUBA  in  the  early  1950's,  direct 
observations  of  kelp  forests  became 
relatively  simple  and,  because  of  mounting 
concern  over  the  effects  of  sewage 
discharges,  loss  of  kelp  habitat,  and 
possible  impacts  of  kelp  harvesting,  a 
number  of  kelp  research  programs  were 
Thus,  giant  kelp  communities 
examined  in  detail  for  only 
more  than  30  years.  The 
of  this  profile  are  to  review 
what  is  known  about  kelp 
emphasis  on  Macrocystis 

have  been 
si ightly 
and  summarize 
forests,  with 

pyrifera  communities  in  California,  and  to 
suggest  future  research  needs  and 
approaches  necessary  to  improve  our 
understanding  of  the  ecology  of  these 
complex  communities. 

Cowardin  et  al .  (1979)  classified 
these  habitats  as  occurring  in  the 
Californian  Province,  marine  system, 
subtidal  subsystem,  aquatic  bed  class, 

algal  bed  subclass,  and  Macrocystis 
dominance  type.  Although  we  recognize  the 
need  for  such  a  classification  system, 
much  of  the  recent  work  on  kelp 
communities  emphasizes  their  considerable 
natural  variation.  Thus,  within  a 
particular  forest  there  may  be  areas  of 
rock  bottom  class  and  unconsolidated  class 
with  most  associated  subclasses  (bedrock, 
rubble,  cobble-gravel,  sand)  and  with 
various  dominance  types  (Laminaria, 
Pterygophora,  various  red  algae,  various 
invertebrates);  the  classification  of  a 
particular  area  may  change  with  time.  The 
modifiers  used  by  Cowardin  et  al.  (1979) 
are  less  variable  in  kelp  forests;  the 
water  regime  is  almost  always  subtidal, 
and  the  water  chemistry  is  euhaline.  We 
have  restricted  our  detailed  review  to  M. 
pyrifera  forests  in  California  (including 
the  Pacific  coast  of  Baje  California, 
Mexico)  because  this  section  of  coastline 
includes  the  entire  geographic  range  of 
the  plant  in  the  northern  hemisphere  (see 
Chapter  1),  because  the  environment  within 
this  range  is  more  similar  than  between  it 
and  other  geographic  areas,  and  because 
most  research  has  been  done  here.  In 
addition,  the  majority  of  the  profile  is 
devoted  to  Macrocystis  itself  because  we 
know  more  about  it  than  other  species  in 
the  community,  because  it  defines  the 
subject  of  the  profile,  and  because  our 
own  work  has  focused  on  it  and  associated 

To  accomplish  the  above  objectives, 
we  have  attempted  to  review  most  of  the 
available  literature  on  California  kelp 
forests,  and  to  compare  and  contrast  this 
information  with  relevant  studies  on  kelp 
forests  and  beds  in  other  areas.  Most  of 
the  early  work  on  Macrocystis  in 
California  is  reviewed  in  North  TT971a). 
We  acknowledge  the  pioneering  work  of 
Wheeler  J.  North,  and  have  relied  heavily 


on  North's  publications  for  information 
prior  to  1971,  and  have  also  focused  on 
reviewing  more  current  information. 

Chapter  1  discusses  the  aims  and 
organization  of  the  profile  in  more 
detail,  and  introduces  the  biology  and 
ecology  of  surface  canopy  kelps,  especial- 
ly Macrocystis  pyrifera.  Physical, 
chemical,  and  geological  aspects  of  the 
kelp  forest  environment  are  reviewed  in 
Chapter-  2.  Chapter  3  describes  community 
structure  and  energetics,  while  Chapter  4 
reviews  the  natural  history  of  organisms 
in  the  community.  Chapter  5  points  out 
some  of  the  problems  with  our  present 
understanding  of  kelp  forest  ecology,  sug- 
gests research  approaches  that  might  solve 
these  problems,  and  critically  examines 
some  current  hypotheses  concerning 
community  structure  and  dynamics.  Chapter 
6  examines  resource  use,  management,  and 
pollution.  Chapter  7  is  a  brief  summary 
and  outlines  research  and  management 

Much  of  the  work  reviewed  concerns 
ecology  and  natural  history  and,  as  a 
result,  the  information  available  is  not 
always  for  a  species.  In  Chapter  6 
especially,  taxonomic  levels  from  species 
(e.g.,  Strongy 1 ocentrotus  f ranci scanus )  to 
combined  phyla  (e.g. ,  sessile  inverte- 
brates) may  be  discussed  in  the  same 
paragraph.  Although  this  is  an  uneven 
treatment,  it  accurately  reflects  the 
state  of  information  for  particular 
organisms.  Species  are  indicated  where 
possible.  In  addition,  because  many  users 
of  this  profile  may  be  unfamiliar  with 

local  species,  we  have  used  widely 
accepted  common  names,  if  available.  The 
scientific  name  is  given  with  the  common 
name  when  the  latter  is  first  used. 
Abbott  and  Hollenberg  (1976;  algae), 
Morris  et  al.  (1980;  invertebrates)  and 
Miller  and  Lea  (1972;  fish)  were  used  for 
names  unless  otherwise  noted  in  the  text. 

The  results  of  much  kelp  forest 
research,  particularly  habitat  surveys  and 
management  problems,  are  published  in 
reports  that  are  often  cited,  but  general- 
ly unreviewed  and  difficult  to  obtain. 
Such  reports  and  other  secondary  scien- 
tific publications  (theses,  unpublished 
manuscripts,  etc.;  see  Day  1983  for  the 
definitions  of  "scientific  papers")  often 
contain  much  useful  information  and  are 
frequently  cited  in  this  profile.  The 
interested  reader  should  obtain  and 
evaluate  these  publications  before  using 
the  information  summarized  from  them  in 
this  profile.  The  names  and  addresses  of 
persons  cited  as  personal  communications 
follow  the  references. 

Comments  on,  or  requests  for,  this 
profile  should  be  addressed  to: 

Information  Transfer  Specialist 
National  Coastal  Ecosystems  Team 
U.S.  Fish  and  Wildlife  Service 
NASA-SI i del  1  Computer  Complex 
1010  Gause  Boulevard 
Slidell,  LA  70458 
504-255-6511,  FTS  685-6511. 







PLATES xiii 




1.1  Taxonomy,  Definitions,  and  Descriptions 2 

1.2  Distribution  4 

1.3  Kelp  Forest  Ecology 5 


2.1  Introduction  9 

2.2  Substratum  and  Sedimentation  9 

2.3  Temperature 11 

2.4  Light 12 

2.5  Nutrients 15 

2.6  Water  Motion 17 


3.1  Introduction 20 

3.2  Distribution  Along  the  Pacific  Coast  of  North  America 22 

3.2.1  Giant  Kelp  Forests 22 

3.2.2  Other  Kelp  Forests 23 

3.3  Distributional  Variation  Among  Sites  23 

3.3.1  Central  California 26 

3.3.2  Southern  California  28 

3.3.3  Other  Geographic  Areas 31 

3.4  Distributional  Variation  Within  Sites 32 

3.4.1  Between  Depths 32 

3.4.2  Within  Depths 32 

3.5  Temporal  Variations  in  Community  Structure  33 

3.5.1  Long-Term 33 

3.5.2  Short-Term 34 

3.5.3  Succession 34 



3.6  Biomass,  Productivity,  and  Energy  Flow  35 

3.6.1  Introduction 35 

3.6.2  Biomass  (Standing  Stocks)  35 

3.6.3  Primary  Productivity 37 

3.6.4  Energy  Flow  -  Food  Webs 39 


4.1  Introduction 43 

4.2  Plankton  and  Decomposers 43 

4.2.1  Phytoplankton 44 

4.2.2  Zooplankton 45 

4.3  Macroscopic  Plants  45 

4.3.1  Introduction 45 

4.3.2  Species  That  Form  Surface  Canopies:  Kelp  Forests  ...  46  Macrocystis  46  Other  Species  That  Form  Surface  Canopies  in 

California  and  Mexico  48  Surface  Canopy  Species  in  Other  Areas  49 

4.3.3  Understory  Canopy  Species:  Kelp  Beds 49  Species  in  California  and  Mexico 49  Species  in  Other  Areas 50 

4.3.4  Bottom  Canopy  Species  52  Fleshy  and  Filamentous  Species 52  Articulated  Corallines 53 

4.3.5  Encrusting  Species 54 

4.3.6  Epiphytes 55 

4.4  Invertebrates 55 

4.4.1  Introduction 55 

4.4.2  Filter,  Suspension,  and  Detritus  Feeders 56  Sponges  56  Cnidarians 56  Bryozoans  57  Brittle  Stars,  Sea  Stars,  Sea 

Cucumbers  and  Sea  Urchins 58  Molluscs 58  Polychaete  Worms 59  Sipunculans  59  Crustaceans  59  Tunicates  60 



4.4.3  Grazers 61  Sea  Urchins  and  Sea  Stars 61  Molluscs 64  Crustaceans  65 

4.4.4  Predators 66  Sea  Stars 66  Molluscs 68  Crustaceans  69 

4.5  Fish 69 

4.5.1  Introduction 69 

4.5.2  Canopy-midwater  Species  70 

4.5.3  Bottom  Species 73 

4.5.4  Other  Species 75 

4.6  Birds  and  Mammals 76 

4.6.1  Birds 76  Introduction 76  Kelp  Forests 76  Drift  Kelp 79  Kelp  Wrack 79 

4.6.2  Marine  Mammals 80  Introduction 80  Sea  Otter 80  Cetaceans  82  Pinnipeds  83  Steller's  Sea  Cow 83 

4.7  Diseases 83 

4.7.1  Introduction 83 

4.7.2  Macroalgae 84 

4.7.3  Invertebrates 84 

4.7.4  Vertebrates 85 


5.1  Introduction 89 

5.2  Effects  of  Temperature 91 

5.3  Effects  of  Water  Motion 93 

5.4  Other  Abiotic  Factors 93 

5.4.1  Depth  Distribution 93 

5.4.2  Variability  Within  Depths  95 



5.5  Effects  of  Competition 97 

5.5.1  Canopy  Removals 97 

5.5.2  Density  of  Macrocystis  Stands  99 

5.5.3  Spore  Dispersal 100 

5.6  Effects  of  Grazing 101 

5.6.1  Invertebrate  Grazers  (other  than  sea  urchins)  102 

5.6.2  Effects  of  Fish 102 

5.6.3  Sea  Urchins 103 

5.7  Indirect  Effects:  Sea  Otter  Foraging 106 


6.1  Introduction:  Management  and  Management  Agencies 108 

6.2  Commercial  Resource  Harvesting  109 

6.2.1  Plants 109  Macrocystis  109  Other  Plants 110 

6.2.2  Animals Ill  Fishes Ill  Abalone  Ill  Sea  Urchins 112  Lobsters 112 

6.2.3  Habitat  Use 113 

6.3  Recreational  Use 113 

6.3.1  Sport  Fishing 113 

6.3.2  Other  Recreational  Activities  113 

6.3.3  Governmental ly  Regulated  Areas 113 

6.4  Scientific  Use 114 

6.5  Pollution  -  Man-Caused  Environmental  Change  Other  Than 

Fishing 114 

6.5.1  Pollution  From  Commercial,  Recreational,  and 

Scientific  Use I14 

6.5.2  Coastal  and  Inland  Construction  114 

6.5.3  Oil 114 

6.5.4  Power  Plant  Discharge  and  Intake 115 

6.5.5  Sewage  Discharge 116 

6.6  Kelp  Forest  Restoration  and  the  Creation  of  New  Kelp  Forests  .  117 

vn  i 


6.6.1  Restoration 117 

6.6.2  Creating  New  Kelp  Forests 118 

6.7  Endangered  Species  119 


7.1  Overview  and  Generalizations  121 

7.2  Management  Recommendations  123 

7.3  Research  Needs 124 


1.  Publications 125 

2.  Addresses  of  Persons  Cited  as  Personal  Communication 150 



Number  Page 

1  The  morphology  and  life  history  of  Macrocystis 3 

2  The  geographic  distribution  of  the  species  of  Macrocystis  5 

3  The  distribution  of  common  seaweeds  within  giant  kelp  forests  ...  6 

4  Water  motion  produced  by  swells  in  shallow  water 17 

5  Factors,  factor  interactions,  and  regulatory  pathways  affecting  the 
algal  associations  in  two  giant  kelp  forests 19 

6  Cross-section  showing  the  inhabitants  of  a  generalized  giant  kelp 
forest 21 

7  The  distribution  of  algae  that  form  surface  canopies  in  the  north- 
east Pacific 22 

8  Location  of  the  ten  kelp  forests  described  in  Chapter  3 23 

9  The  distribution  of  conspicuous  plants  and  animals  found  in  five 
central  California  kelp  forests  24 

10  The  distribution  of  conspicuous  plants  and  animals  found  in  five 
southern  California  kelp  forests 25 

11  A  generalized  food  web  for  a  kelp  forest 40 

12  A  food  web  for  the  Point  Cabrillo  kelp  forest 41 

13  Generalized  control  web  of  factors  and  interactions  affecting  the 
distribution  and  abundance  of  organisms  in  a  kelp  forest 42 

14  Common  benthic  diatoms  and  a  mysid  shrimp  44 

15  A  survivorship  curve  for  Macrocystis  pyrifera  47 

16  Colonization  times  for  the  more  abundant  algal  species  that  re- 
cruited to  artificial  substrata  in  a  kelp  forest  at  Santa  Cruz 
Island 53 

17  Common  understory  algae  54 

18  Relationship  between  the  canopy  cover  of  Macrocystis  and  upright 
(non-encrusting)  understory  algal  cover  54 


Number  Page 

19  Invertebrate  filter,  suspension,  and  detritus  feeders  common  in 

kelp  forests 56 

20  Common  invertebrate  grazers  in  kelp  forests 60 

21  Some  common  invertebrate  predators  in  kelp  forests  68 

22  Some  common  kelp  forest  fishes 70 

23  Birds  commonly  associated  with  kelp  forests 78 

24  Marine  mammals  associated  with  kelp  forests 80 

25  The  gauntlet  of  Macrocystis  life  history  stages 90 

26  Kelp  forest  dynamics  and  temporal  and  spatial  scales  91 

27  Temperature  and  irradiance  recorded  on  the  bottom  in  a  Macro- 
cystis forest  over  a  4-year  period 92 

28  Field  station  used  for  Macrocystis  pyrifera  gametophyte  outplants.  94 

29  Irradiance-temperature  response  surface  for  Macrocystis  pyrifera 
sporophyte  recruitment  96 

30  Kelp  harvesting  ship 109 

31  Aerial  photograph  of  oil  spill  in  a  giant  kelp  canopy 115 



Number  Page 

1  Factors  influencing  kelp  forest  algal    populations   7 

2  Light  levels  for  compensation  and  saturation  of  growth  in  various 
stages  of  Macrocystis   13 

3  Known  nutrient  requirements  for  Macrocystis  pyrifera 15 

4  Kelp  forest  biomass 36 

5  Macrocystis  net  primary  productivity 38 

6  Common  invertebrate  grazers   62 

7  Concentration  and  biomass  of  two  sea  urchin  species  across  a 
grazing  band 64 

8  Common  invertebrate  predators  found  in  Macrocystis  forests.    ...  66 

9  Subhabitat  and  feeding  categories  of  common  kelp  forest  fishes.    .  71 

10  Birds  of  kelp  forests 77 

11  Outline  of  a  factorial    laboratory  experiment 97 

12  Abalone,  lobster,  and  sea  urchin  landings  in  California 112 



Number  Page 

A  giant  kelp  forest  at  Santa  Catalina   Island  Cover 

1A  Macrocystis  surface  canopy  near  Santa  Barbara 87 

IB  Infra-red  aerial    photograph  of  Macrocystis   (orange)   canopy 

in  Carmel    Bay 87 

1C  Macrocystis  forest  with  numerous  fish  beneath  the  surface 

canopy 87 

ID    Pelagophycus  porra  at  Santa  Catalina  Island 87 

IE    Understory  canopy  of  Pterygophora  californica 87 

IF    The  articulated  coralline  alga  Calliarthron,  and  the  purple- 
ringed  top  shell  Calliostoma  annulatum 87 

2A    The  lined  chiton  Tonicella  lineata  on  an  encrusting  coralline 

alga 88 

2B    Cup  corals  and  the  cobalt  sponge  Hymenamphiastra 88 

2C    Various  tunicates  and  sponges  on  a  vertical  wall  within  a  kelp 

forest 88 

2D  Red  sea  urchins  surrounded  by  various  foliose  red  algae  ....   88 

2E  Pisaster  giganteus  and  a  group  of  strawberry  anemones,  Cory- 

nactis  cal  ifornica 88 

2F  The  hydrocoral  Allopora  californica   88 



Metric  to  U.S.   Customary 

Mul tiply 

mill imeters  (mm) 
centimeters  (cm) 
meters  (m) 
kilometers  (km) 

square  meters  (m  ) 
square  kilometers  ( km  ) 
hectares  (ha) 

liters  (1) 
cubic  meters 
cubic  meters 


mil  1 igrams  (mg) 
grams  (g) 
kilograms  (kg) 
metric   tons  (t) 
metric  tons 
kilocalories  (kcal ) 

Celsius  degrees 


To  Obtain 








mil  es 


square  feet 


square  mil  es 




gal  Ions 


cubic  feet 


acre- feet 










short  tons 


British  thermal    units 

1.8(°C)    +  32 

Fahrenheit  degrees 

U.S.  Customary  to  Metric 





feet  (ft) 




miles  (mi) 


nautical   miles  (nmi) 


square   feet  (ft2) 




square  miles  (mi    ) 


gallons  (gal ) 


cubic  feet  (ft3) 


acre- feet 


ounces  (oz) 


pounds  (lb) 


short  tons  (ton) 


British  thermal    units  (Btu)           0.2520 

Fahrenheit  degrees 

0.5556(°F  -  32) 

mill imeters 






square  meters 


square  kilometers 


cubic  meters 
cubic  meters 

metric  tons 
kil ocalories 

Celsius  degrees 



We  are  indebted  to  numerous  people 
who  assisted  in  the  preparation  of  this 
profile.  G.  Van  Dykhuizen  wrote  the  first 
draft  of  the  fish  section,  and  T.  Keating 
the  first  draft  of  the  birds  and  mammals 
section.  The  investigators  listed  in 
Section  2  of  References  generously  shared 
their  unpublished  observations  with  us. 
Complete,  detailed  reviews  by  C.  Harrold 
and  G.  VanBlaricom  were  especially  useful 
in  revising  the  manuscript.  All  or  parts 
of  the  entire  profile  were  also  read  by  N. 
Andrew,  D.C.  Barilotti,  W.J.  Ballantine, 
R.  Brown,  M.  Carr,  R.  Cowen,  P.  Dayton,  T. 
Dean,  L.  Deysher,  A.  DeVogelaere,  A. 
Ebeling,  J.  Estes,  Z.  Hymanson,  S. 
Kennelly,  S.  Kimura,  E.  Low,  M.  Neushul , 
A.  Perry,  D.  Reed,  L.  Stocker,  and  J. 
Watanabe,  and  we  thank  them  for  their 
helpful  suggestions.  R.  Stelow  and  C. 
King  typed  the  manuscript,  L.  McMasters 

drafted  most  of  the  drawings,  and  S. 
Dearn,  M.  Tomasi ,  and  G.  Van  Dykhuizen 
helped  compile  the  references.  D.  Schiel 
was  partially  supported  by  the  Claude 
McCarthy  Foundation  of  the  University 
Grants  Committee,  New  Zealand,  by  the 
University  of  Auckland,  and  by  the 
U.S.N.Z.  Cooperative  Science  Program. 

Special  thanks  go  to  J.  Cooper  of  the 
U.S.  Fish  and  Wildlife  Service  for 
encouraging  us  to  write  the  profile,  and 
to  W.  Kitchens  of  the  U.S.  Fish  and 
Wildlife  Service  for  his  support, 
suggestions,  and  patience. 

Each  of  us  particularly  acknowledges 
the  person  who  most  influenced  our  early 
work  and  views  on  kelp  forest  ecology.  To 
Michael  Neushul  (MSF)  and  Howard  Choat 
(DRS),  we  extend  our  special  thanks. 




/  know  few  things  more  surprising  than  to  see  this  plant  grow- 
ing and  flourishing  amidst  those  breakers  of  the  western  ocean, 
which  no  mass  of  rock,  let  it  be  ever  so  hard,  can  long  resist. 
Darwin  (1860). 

This  profile  is  about  large  brown 
algae  of  the  genus  Macrocystis  and 
organisms  associated  with  them  in  subtidal 
habitats  along  the  west  coast  of  North 
America.  Historical  interest  in  giant 
kelp  was  stimulated  by  its  wide  geographic 
distribution,  particularly  in  the  southern 
hemisphere,  and  by  the  immense  size  of  the 
plants.  As  early  as  the  1600's,  European 
mariners  used  Macrocystis  as  a  naviga- 
tional aid:  the  presence  of  a  floating 
canopy  of  attached  plants  indicated 
shallow  reefs,  while  floating  bundles  of 
drift  plants  indicated  that  the  coast  was 
not  far  off  (North  1971b). 

The  relatively  easy  harvesting  of 
plants  made  them  the  basis  of  the  potash 
industry  in  the  United  States  during  the 
First  World  War.  At  present,  some  150,000 
wet  tons  are  harvested  annually,  mostly 
for  the  extraction  of  algin,  a  hydro- 
colloid  (Frey  1971).  The  recreational  and 
aesthetic  value  of  these  plants  is  also 
recognized  now  because  of  the  association 
between  them  and  many  desirable  food 
species  of  fish  and  shellfish.  Mammals 
such  as  sea  otters  and  harbor  seals,  as 
well  as  numerous  birds,  also  commonly 
occur  in  these  habitats.  The  disappear- 
ance of  a  large  tract  of  Macrocystis  off 
the  Palos  Verdes  Peninsula  (Los  Angeles 
County)  and  from  other  areas  of  southern 
California  in  the  1950's  brought  an  aware- 
ness that  these  stands  may  be  ephemeral  in 
nature  and  particularly  disturbed  by 
pollution  associated  with  large  centers  of 
population.   This  spawned  a  series  of 

research  programs  to  study  life  history 
features  of  giant  kelp  and  its  associated 
organisms.  It  became  apparent  that  many 
factors  were  responsible  for  the  variation 
in  kelp  abundance.  Variation  through  time 
was  assessed  by  estimates  of  the  cover  of 
the  surface  canopy  of  Macrocystis  in 
several  localities  (North  1967,  19691. 

Differences  in  coverage  between 
surveys  were  ascribed  to  human  pertur- 
bation such  as  sewage  outfalls  (Wilson 
1982),  to  warm  water  (North  1971b),  and  to 
grazers  such  as  sea  urchins  (Leighton 
1971;  see  Foster  et  al.  1983  for  review). 
It  was  also  clear  that  the  temporal  and 
spatial  variation  in  Macrocystis  abundance 
was  controlled  not  by  a  single  factor  but 
by  numerous  factors,  some  acting  in 

It  is  our  aim  to  describe  the  giant 
kelp  forest  environment  and  to  discuss  the 
sources  of  variability  in  the  distribution 
and  abundance  of  the  organisms  in  it, 
especially  Macrocystis  (see  Preface).  Be- 
sides geographic  and  temporal  differences 
in  plant  abundance,  great  spatial  differ- 
ences in  distribution  are  also  evident  at 
any  one  locality.  Even  in  areas  where 
hard  substratum  is  available,  any  particu- 
lar alga  is  usually  restricted  to  a 
relatively  narrow  range  of  depths  (e.g., 
McLean  1962,  Neushul  1967).  This  sort  of 
distribution  can  be  the  result  of  the 
interactions  of  many  abiotic  factors  such 
as  light  and  temperature  change  with 
depth,  and  biological  factors  such  as 

competition  for  space  with  other  species. 
Even  within  sites  of  similar  depth  at  one 
locality,  other  factors  such  as  amounts  of 
sediment  covering  the  substratum  and  the 
presence  of  grazers  may  differ  on  a  small 
spatial  scale,  resulting  in  a  small-scale 
variation  in  the  presence  and  abundance  of 
algae.  Each  of  these  factors  may  act  on  a 
different  life  history  stage  of  a  species. 
Because  both  biotic  and  abiotic  factors 
may  change  over  small  distances,  the 
pattern  of  algal  distribution  and  abun- 
dance may  change  from  locality  to  locality 
(see  Chapter  3).  Moreover,  some  of  this 
pattern  may  result  from  stochastic  pro- 
cesses, large  scale  phenomena  (Dayton  and 
Tegner  1984a),  and  historical  events  that 
are  difficult  to  study. 

We  have  generally  taken  a  functional 
approach  in  discussing  the  organisms  in 
Macrocystis  communities,  as  floristic  and 
faunistic  species  checklists  may  be  found 
in  other  sources  (see  Chapters  3  and  4). 
We  discuss  many  species  and  environmental 
factors,  assessing  their  interactions  with 
Macrocystis  and,  where  possible,  their 
influence  on  some  phase  or  phases  of  the 
life  cycle  of  Macrocystis.  It  is  our 
intention  to  influence  the  direction  of 
future  field-based  studies  involving 
Macrocystis.  Research  to  date  has  gone 
through  qualitative  and  descriptive 
phases,  with  a  relatively  small  amount  of 
experimental  work.  We  hope  to  see  more 
carefully  conceived  sampling  and  experi- 
mental research  featuring  specific 
hypotheses  with  replication  and  proper 
controls.  We  synthesize  the  extant  liter- 
ature and  technical  reports  with  this  in 
mind,  and  include  accounts  of  work  in 
progress  in  several  California  localities. 


The  taxonomy  of  Macrocystis  has  been 
argued  since  the  genus  was  first  named  by 
C.A.  Agardh  (1820,  1839),  and  has  been 
reviewed  by  Womersley  (1954),  Neushul 
(1971a),  and  Brostoff  (1977).  C.A.  Agardh 
recognized  six  species,  based  on  blade  and 
float  characteristics  of  what  were  proba- 
bly drift  specimens  (Agardh  1839).  Hooker 
(1847)  decided  that  only  one  species 
existed,  M.  pyrifera.  Howe  (1914)  was  the 
first  to  use  the  now  commonly  accepted 
system  of  holdfast  characteristics  to 

separate  another  species,  H.  integrifol ia 
(Howe  1914,  Setchell  1932,  Womersley 
1954).  Womersley  (1954)  used  holdfast 
characteristics  to  decide  that  a  third 
species,  M.  angustifol ia,  existed  in 
Australia  and  Africa.  The  holdfasts  of 
these  currently  recognized  species  are 
illustrated  in  Figure  IA.  Neushul  (1971a) 
mapped  the  distribution'  of  the  three 
species  in  the  northern  hemisphere,  with 
M.  integrifol ia  occurring  north  from 
Monterey,  California  to  Sitka,  Alaska;  M. 
angustifol ia  occurring  in  central 
California  and  perhaps  southern 
California;  while  M.  pyrifera  was  distri- 
buted in  southern  Cal ifornia.  Brostoff 
(1977)  concluded,  based  on  detailed  mor- 
phological comparisons  and  transplant 
experiments,  that  the  California  M. 
angustifolia  described  by  Neushul  (1971a) 
should  be  designated  _M.  pyrifera  var. 
cal ifornica,  with  M.  pyrifera  becoming  M. 
pyrifera  var.  pyrifera.  Abbott  and 
Hollenberg  (1976),  however,  recognize  only 
two  species  of  Macrocystis  from 
California,  M.  pyrifera  in  the  subtidal 
zone  and  M.  integrifol ia  in  the  low 
intertidal-shal low  subtidal  zone.  For  the 
purposes  of  this  profile,  we  will  abide  by 
the  Abbott  and  Hollenberg  (1976)  classifi- 
cation; references  to  "giant  kelp  forests" 
mean  subtidal  M_.  pyrifera  communities 
found  on  the  west  coast  of  North  America. 

A  few  other  terms  are  used  throughout 
this  book,  so  it  would  be  useful  to  define 
them  here.  Almost  every  paper  concerning 
Macrocystis  mentions  the  rapid  growth 
rates  of  individual  fronds.  Early  des- 
criptions also  noted  the  great  sizes  of 
plants.  The  name  "giant  kelp"  has 
remained  the  common  designation  of  the 
species  of  Macrocystis.  Because  of  the 
great  sizes  of  individual  plants,  their 
trunk-like  appearance  in  the  water  column 
(see  cover  photo),  and  the  surface 
canopies  which  can  be  extensive  along 
coastlines,  these  areas  of  subtidal 
habitat  have  been  called  "forests"  and  we 
will  use  this  term.  A  "stand"  refers  to 
any  localized  group  of  plants.  "Community 
structure"  is  used  as  a  general  term  that 
includes  the  species  composition,  abun- 
dance, and  three-dimensional  distribution 
of  organisms  in  a  kelp  forest.  "Community 
dynamics"  refers  to  change  in  structure 
with  time. 

Holdfast  morphology  of  Macrocystis  spp. 
(redrawn  from  Neushul  1971a) 

-haptera  ^-^T~>^ 


M.  pyrifera         M.  angustifolia         M.  integrif olia 


Morphology  and  life  history  of  M.  pyrifera 
(modified  from  Dawson  and  Foster  1982) 

blade  with 
(sporophyl  !).■;'_" 


sporangium  (2N) 

.  zoospore (N) 

r)x     p  s    young 



<$  gametophyte 



diploid  (2N) 






O  gametophyte 
*  CN] 





Figure  1.   The  morphology  and  life  history  of  Macrocystis. 

Dense  stands  of  Macrocystis  provide  a 
vertically-structured  habitat  through  the 
water  column,  and  may  have  a  considerable 
shading  effect  on  the  organisms  below. 
These  stands  also  provide  nurseries,  feed- 
ing grounds  and/or  protective  cover  for 
many  other  organisms.  Darwin  (1860) 
referred  to  them  as  great  aquatic  forests 
of  the  southern  hemisphere,  comparing  them 
in  complexity  to  terrestrial  forests. 
Thus,  giant  kelp  forests  have  come  to  mean 
the  areas  of  coastline  featuring  extensive 
coverage  by  the  surface  canopy  of 
Macrocystis.   Other  kelps  (using  a  re- 

stricted definition  of  "kelp"  as  members 
of  the  Order  Laminariales)  that  form  sur- 
face canopies  in  temperate  and  polar  re- 
gions may  also  form  quite  dense  forests, 
but  their  tissue  floating  on  the  surface 
of  the  sea  tends  not  to  be  as  extensive  as 
that  of  Macrocystis  (see  Section  3.2.2). 
We  will  refer  in  general  to  communities 
with  surface  canopy  kelps  as  "kelp 
forests,"  those  with  primarily  Macrocystis 
as  "giant  kelp  forests,"  and  those  with 
other  particular  kelps  as  "bull  kelp 
forests,  etc."  depending  on  the  genus  or 

Kelps  that  produce  surface  canopies 
usually  have  floats  (pneumatocysts)  or 
other  gas-filled  structures  for  buoyancy. 
Numerous  other  kelps  lack  such  structures 
and  do  not  form  a  surface  canopy  except  at 
low  tide  if  they  are  growing  in  very 
shallow  (1-2  m  deep)  water.  They  may, 
however,  form  dense  canopies  up  to  a  few 
meters  above  the  substratum  to  which  they 
are  attached.  Extensive  stands  of  these 
smaller  laminariales  occur  in  all 
temperate  and  some  polar  regions  of  the 
world.  Conventionally,  these  stands  are 
referred  to  as  kelp  "beds,"  recognizing 
subjectively  that  the  vertical  structure 
is  not  so  extensive  as  it  is  for  those 
species  forming  surface  canopies.  Com- 
munities featuring  dense  stands  of 
Laminaria  spp.  have  been  studied  in  Nova 
Scotia  ("Mann  1972a,  b,  Breen  and  Mann 
1976,  Chapman  1981),  and  the  British  Isles 
(Kain  1979).  In  the  southern  hemisphere, 
Ecklonia  spp.  have  been  studied  in  New 
Zealand  (Choat  and  Schiel  1982),  Australia 
(Shepherd  and  Womersley  1970,  1971, 
Kennelly  1983),  and  South  Africa 
(Velimirov  et  al.  1977).  These  beds  are 
analogous  to  kelp  forests  but  without  a 
surface  canopy,  and  the  principles  of 
sampling  and  experimenting  in  them  should 
be  no  different  than  in  giant  kelp  for- 
ests. We  have  drawn  on  this  literature 
for  comparisons  with  work  in  Macrocystis 

Macrocystis  belongs  to  the  Order 
Laminariales,  Family  Lessoniaceae.  It  has 
a  typical  laminarian  life  cycle  (Figure 
IB),  with  microscopic  haploid  spores  (IN) 
developing  into  male  and  female  gameto- 
phytes  (IN).  Eggs  on  female  gametophytes 
are  fertilized,  and  the  zygotes  develop 
into  the  macroscopic  diploid  sporophytes 
(2N).  On  mature  plants,  clusters  of 
sporophylls  containing  reproductive  tissue 
(sori)  are  found  on  the  lower  portion  of 
plants  just  above  the  holdfasts  (Figure 
lb).  Fronds  (stipes  with  associated 
floats  and  blades)  comprise  the  large 
portion  of  plants  which  are  seen  in  the 
water  column,  and  floating  on  the  surface 
of  the  sea.  Further  descriptions  of  the 
life  cycle  and  morphology  of  Macrocystis 
can  be  found  in  Abbott  and  Hollenberg 
(1976)  and  Lobban  (1978). 


Subtidal  forests  of  Macrocystis  occur 
in  many  areas  of  the  world,  but  are  most 
widely  distributed  in  the  southern  hemi- 
sphere (Figure  2).  Populations  exist  in 
the  southern  hemisphere  along  the  east  and 
west  coast  of  South  America,  off  South 
Africa,  Tasmania  and  south  Australia,  New 
Zealand,  and  the  sub-antarctic  islands. 
As  with  other  species  with  bipolar  distri- 
butions, it  is  generally  thought  that 
temperature  is  the  chief  barrier  to  the 
geographic  expansion  into  warmer  waters 
(Hedgpeth  1957).  However,  recent  work  has 
shown  an  inverse  relationship  between 
temperature  and  nutrients,  so  low  nutri- 
ents may  be  the  important  factor  (see 
Sections  2.3  and  2.5).  In  contrast, 
Gaines  and  Lubchenco  (1982)  suggest  that 
herbivory  increases  inversely  with  lati- 
tude, so  extension  into  warmer  waters  may 
also  be  limited  by  grazing.  A  combination 
of  cold  water  and  low  light  levels  acting 
on  the  various  life  history  stages  of 
plants  probably  prevents  expansion  of 
ranges  toward  the  poles  (Van  den  Hoek 
1982).  North  (1982)  suggested  that  the 
genus  evolved  in  the  southern  hemisphere 
and  its  bipolar  distribution  in  the 
Pacific  (but  not  the  Atlantic)  may  be  the 
result  of  a  cold  water  "bridge"  in  the 
geologic  past  (North  1971b).  In  contrast, 
Estes  and  Steinberg  (MS.)  point  out  that 
all  but  one  of  the  presently  recognized 
genera  in  the  Order  Laminariales  occur  in 
the  North  Pacific,  and  suggest  a  North 
Pacific  origin  and  subsequent  southern 
migration  for  these  kelps,  including 

Populations  of  Macrocystis  in  the 
North  Pacific  extend  from  Alaska  to  local- 
ities of  upwelled  cooler  water  in  Baja 
California,  Mexico  (Druehl  1970;  see 
Chapter  3).  Macrocystis  pyrifera  is  found 
from  near  Santa  Cruz  in  central  California 
to  Baja  California,  Mexico  (Druehl  1970). 
Abbott  and  Hollenberg  (1976)  give  Alaska 
as  the  northern  limit,  but  Druehl  (1970) 
is  probably  correct  as  we  have  never 
observed  the  species  much  beyond  Santa 
Cruz,  and  could  find  no  other  reports  of  a 
more  northern  distribution. 






'     <*$J "^ ^~ r 





60°   - 

••••M.angustifolia    Jj 

mill  M.mtegrifolia 

—  M.pyrifera  I  Una 


Figure  2.    The  geographic  distribution  of  the  species  of  Macrocystis  (redrawn  from 
Womersley  1954). 

Besides  geographic  limits  to  distri- 
bution, there  are  also  limitations  within 
localities.  Marine  plants  are  depth 
restricted.  Early  surveys  using  SCUBA 
identified  various  zones  similar  to  those 
in  intertidal  regions  (McLean  1962, 
Neushul  1967,  Aleem  1973;  see  Chapter  3). 
Stylized  diagrams  of  depth  distribution 
resulted  in  composite  pictures,  such  as 
those  in  Figure  3.  Surf  grass  (Phyllo- 
spadix  spp.)  is  often  found  in  very 
shal low  subtidal  areas,  with  another  kelp, 
Egregia  menziesi  i ,  also  occupying  the 
turbulent  inshore  sites.  Several  kelps 
may  inhabit  intermediate  depths  (4-15  m 
deep).  Macrocystis  pyrifera  does  not 
generally  extend  into  very  shallow  water, 
or  to  depths  below  ^  20  m  in  the  turbid 
coastal  waters.  Figure  3  presents  only  a 
crude  picture  of  depth  distribution.  It 
is  interesting  that  there  are  no  published 
studies  which  have  quantified  both  the 

abundances  and  depth  distribution  of  con- 
spicuous species  of  algae  at  different 
sites  in  California.  Such  a  sampling 
program  would  result  in  a  more  solid 
framework  for  posing  hypotheses  about  kelp 
forest  dynamics,  in  much  the  same  way  that 
good  experimental  intertidal  studies  are 
based  on  detailed  knowledge  of  the  distri- 
butions and  abundances  of  organisms 
(Dayton  1971,  Connell  1972,  Underwood  et 
al.  1983). 


Distributional  studies  should  be 
concerned  with  the  numerical  abundances  of 
plants  of  a  species  in  different  loca- 
tions. A  single  plant  of  a  species  such 
as  Macrocystis  may  have  a  much  larger 
impact  on  the  rest  of  the  community  than  a 
single  understory  kelp.  Nevertheless,  the 
presence  or  absence  of  a  kelp  forest  is 

18  (60) 




Figure  3.  The  distribution  of  some  common  seaweeds  within  giant  kelp  forests.  Plants 
in  the  four  zones  of  vegetation  layering  include  (1)  small  filamentous  species  and 
encrusting  coralline  algae;  (2)  bottom  canopy  plants  such  as  Gel idium,  Cal 1 iarthron, 
and  Plocamium;  (3)  understory  canopy  kelps  such  as  Pterygophora,  Eisenia,  and 
Laminaria;  and  (4)  midwater  and  surface  canopy  plants  such  as  Egregia,  Macrocystis,  and 
Nereocystis.  This  is  a  generalized  diagram  and  some  species  do  not  co-occur  in  the 
same  site  (modified  from  Dawson  and  Foster  1982). 

essentially  the  result  of  a  "numbers 
game":  How  many  plants  are  in  an  area? 
How  fast  do  they  grow?  How  long  do  they 
live?  What  is  their  reproductive  output? 
How  many  new  recruits  appear?  Plants  also 
respond  differently  when  placed  in  differ- 
ent conditions,  such  as  those  which  occur 
naturally  at  different  localities,  and  at 
different  depths  within  the  same  locali- 
ties. These  sorts  of  demographic 
questions  remain  to  be  answered  primarily 
by  field-based  studies. 

This  approach  has  generally  not  been 
followed  in  giant  kelp  forest  research, 
and  there  is  a  definite  bias  in  the 

literature  in  studies  done  j_n  situ  with 
Macrocystis.  Most  field  research  has  been 
done  at  a  very  few  sites  (near  Point  Loma, 
San  Diego  County;  the  Palos  Verdes  area, 
Los  Angeles  County;  and  near  Santa 
Barbara)  to  resolve  questions  about 
habitat  loss  and  restoration.  This  is  due 
to  historic  reasons,  including  the  large 
population  centers  in  southern  California, 
kelp  harvesting  in  the  area,  the  presence 
of  several  universities  with  facilities 
for  marine  research,  a  sudden  awareness  of 
environmental  problems  coincident  with  the 
increase  in  sewer  discharges,  and  the 
disappearance  of  large  kelp  forests  on  the 
Palos  Verdes  Peninsula  and  near  Point 

Loma.  A  succession  of  programs  developed 
to  study  southern  California  kelp  forest 
communities  and  to  restore  Macrocystis  in 
areas  where  it  was  formerly  abundant.  The 
Institute  of  Marine  Resources  sponsored 
programs  from  1956  to  1963;  the  Kelp 
Habitat  Improvement  Project  investigated  a 
number  of  problems  from  1964  to  1976;  and 
recently,  the  California  Department  of 
Fish  and  Game  assumed  responsibility  for 
restoring  coastal  habitats  (see  Chapter 
6).  In  addition,  this  work  became  partic- 
ularly concerned  with  the  interactions  of 
sea  urchins  and  kelp  (North  1983a).  Dense 
aggregations  of  sea  urchins  dislodged 
Macrocystis  plants  that  subsequently 
drifted  away  (Leighton  1971).  The  major 
problem  is  that  once  plants  have  been 
removed  by  any  cause,  drift  material  de- 
clines, sea  urchins  apparently  begin  to 
forage  actively  for  food,  and  this 
intensive  grazing  may  prevent  the  re- 
establishment  of  kelp  populations  for  some 
time  (see  Chapter  5).  This  has  resulted 
in  many  programs  to  destroy  sea  urchins 
(Wilson  and  McPeak  1983). 

The  problems  of  controlling  and 
managing  what  was  seen  as  a  resource 
eventually  highlighted  the  need  for  work 
to  assess  the  importance  of  other  factors. 
In  addition,  recent  work  on  giant  kelp 
forests  in  central  California  (Pearse  and 
Hines  1979,  Cowen  et  al.  1982,  Foster 
1982a),  South  America  (Barrales  and  Lobban 
1975,  Santelices  and  Ojeda  1984a,  b),  and 
southern  California  (Dean  and  Deysher 
1983,  Dayton  et  al.  1984)  has  begun  to 
provide  a  broader  perspective  on  the 
ecology  of  these  communities.  Table  1 
presents  a  summary  of  factors  which  have 
been  suggested  or  observed  to  affect  the 
presence  and  abundance  of  kelp  plants  (see 
Chapters  2,  3,  and  4  for  details).  The 
effects  of  most  of  these  are  not  known, 
except  in  broad  outline.  The  basic 
resources  of  space,  light,  and  nutrients 
may  be  altered  by  differing  biotic  and 
abiotic  conditions.  Moreover,  we  have 
little  idea  of  how  different  levels  or 
combinations  of  these  factors  affect  plant 
recruitment,  growth,  reproduction,  and 
survival.  These  issues  are  discussed  in 
detail  in  the  following  chapters. 

Table  1.      Factors  influencing  giant  kelp  forest  algal  populations  with  emphasis  on 
Macrocystis  pyrifera  in  California. 




Sedimentation  and 
sand  movement 

Required  for  attachment 

Hardness  related  to  mortality  due  to  water  motion 
Topographic  heterogeneity  correlated  with  distribution  and 

Attachment  and  survivorship,  especially  of  microscopic  life  stages 

Burial  of  all  or  portions  of  organisms 



Water  motion 


Survival  and  growth  of  plants,  at  least  1%   of  surface  for  kelps 
Gametogenesis  in  kelps 

Plant  and  animal  loss  in  surge  and  currents 
Distribution  of  food  (plankton  and  detritus) 
Nutrient  availability  and  uptake 

Growth  and  fertility  of  plants  and  animals 

Growth  of  benthic  plants  (and  phytoplankton) 



Table  1.  Concluded. 

Factor  Influence 

Toxic  substances: 
Cu  Reduced  Microcystis  growth  and  reduced  fertility  at  30  ppb 

DDT  Possible  general  alteration  of  community 

Diseases  of: 

Plants  Occur,  but  population  effects? 

Urchins  Can  cause  massive  mortality 

Sea  stars  Occur,  can  cause  massive  mortality 

Fish  Occur,  but  population  effects? 

Grazing  by: 

Fish  Can  destroy  Macrocystis   if  plants  at  low  density 

Sea  urchins  Can  create  areas  of  varied  size  nearly  devoid  of  foliose  macroalgae 

Isopods  May  destroy  canopy  and  sub-canopy  tissue 

Other  grazers  Consume  small    life  history  stages.     Population  effects? 

Predation  Sea  stars,   sheephead,     sea  otters  and  other  predators,   including 

humans,  may  affect  the  distribution  and  abundance  of  a   variety  of 
Sea  stars  and  fishes  may  alter  plant-sessile  animal    competition 

Competition  Canopy  shading   inhibits  understory  algal    recruitment  and  growth 

within  and  among  species 
Pre-emption  of  space 
Whiplash  effects  of  algal    fronds 
Competition   for  space  and  light  affects  distribution  of  sessile 

Competition  (including  behavior)  affects  fish  distribution 



Environmental  factors  involved  in  seaweed  ecology — light, 
nutrients,  water  motion,  and  temperature — have  similar  stratified 
distributions.  As  a  result,  it  is  difficult  to  determine  which  are 
the  key  factors.  But  it  is  easy  to  find  a  relationship  of  any  one 
with  algal  distribution.  Jackson  (1977). 


The  existence  of  a  giant  kelp  forest 
depends  upon  physical  and  chemical  condi- 
tions that  favor  the  reproduction  and 
growth  of  Macrocystis.  With  few  excep- 
tions, this  abiotic  environment  includes  a 
hard  substratum,  water  temperatures  gener- 
ally <  20  °C,  bottom  light  intensities 
equivalent  to  \%  of  surface  irradiance  or 
greater,  adequate  nutrients,  oceanic 
salinities,  and  protection  from  extreme 
water  motion. 

Much  of  the  Pacific  coast  of 
California  and  Baja  California,  Mexico 
(Figure  2)  fulfills  these  criteria. 
Nearshore  waters  to  the  north  may  be  too 
exposed  to  water  motion,  while  those  to 
the  south  are  probably  too  warm  or  low  in 
nutrients  (see  Sections  2.3  and  2.5).  The 
outer  coast  within  the  range  of  Macrocys- 
tis is  moderately  exposed  to  oceanic 
swells,  salinity  is  relatively  constant  at 
around  33  ppt,  and  surface  temperatures 
vary  from  a  seasonal  low  of  8  °C  around 
Monterey  to  a  seasonal  high  of  around  24 
CC  in  Baja  California  (Section  2.3).  In 
the  southern  part  of  this  range,  kelp 
forests  are  particularly  well  developed  in 
cool,  nutrient-rich  upwelling  areas. 
Plants  commonly  occur  at  depths  between  5 
and  20  m.  The  community  may  develop  on 
almost  any  rocky  bottom  within  these 
limits;  the  absence  of  Macrocystis 
commonly  indicates  an  unstable  bottom. 

Macrocystis  is  usually  not  found  in 
estuaries  or  very  far  inside  protected 
bays.  The  reasons  for  its  absence  in  such 
habitats  have  not  been  investigated,  but 
are  probably  related  to  factors  such  as 
lack  of  rocky  substrata,  decreased  light, 
increased  sedimentation,  and  reduced 
salinity.  North  (1969)  reported  severe 
damage  to  adult  giant  kelp  transplants  in 
Newport  Bay  when  salinity  was  lowered  to 
10  ppt  during  a  storm.  North  (pers. 
comm.)  has  also  found  that  cultured 
gametophytes  do  not  survive  at  salinities 
below  25  ppt. 

In  the  rest  of  this  chapter  we 
discuss  the  abiotic  environment  in  detail 
for  Macrocystis.  The  abiotic  conditions 
necessary  for  other  organisms  are  also 
described  but,  in  most  cases,  very  little 
information  is  available. 


With  few  exceptions,  the  sessile 
organisms  associated  with  giant  kelp  for- 
ests require  a  hard  substratum  for 
attachment.  If  these  plants  and  animals 
do  manage  to  attach  and  grow  on  sediment, 
they  are  usually  swept  away  in  all  but 
very  calm  water.  Extensive  areas  of 
cobble  and  boulder  occur  between  Oceanside 
and  Del  Mar  in  southern  California,  and 
adult  Macrocystis  in  this  region  commonly 
grow  on  these  substrata,  particularly  in 

the  vicinity  of  San  Onofre.  If  water 
motion  is  great  enough,  the  drag  on  these 
and  other  kelps  is  sufficient  to  dislodge 
them  and  their  substrata  from  the  bottom. 
These  plants  plus  cobble  "anchors"  may 
re-establish  elsewhere  if  conditions  are 
suitable,  or  be  transported  to  the  beach 
or  to  deeper  water  (SCE  1982). 

In  areas  of  extensive  rocky  reefs, 
the  hardness  of  the  substratum  is  also 
important;  organisms  growing  on  soft  rock 
such  as  mudstone  may  be  dislodged  because 
drag  on  the  plants,  induced  by  water 
movement,  fractures  the  rock.  Differences 
in  community  composition  in  central 
California  may  partially  result  from 
differences  in  rock  type  (Foster  1982a). 

The  major  exceptions  to  this  occur- 
rence on  rocky  substrata  are  kelp  forests 
in  the  vicinity  of  Santa  Barbara,  where 
Macrocystis  commonly  grows  attached  to 
sediment  ("Thompson  1959,  Neushul  1971a, 
North  1971b).  Neushul  (1971a)  suggested 
that  young  plants  first  establish  on  solid 
surfaces  such  as  worm  tubes.  As  the 
plants  grow,  anchorage  is  increased  by 
sediment  partially  covering,  and  accumu- 
lating in,  the  holdfast.  These  holdfasts 
can  be  over  a  meter  in  diameter,  and 
Barilotti  (pers.  comm. )  found  that,  once 
holdfasts  are  established,  they  become  the 
primary  site  for  subsequent  new  recruit- 
ment. The  large  size  of  the  holdfasts 
probably  results  from  the  accumulation  of 
haptera  from  successive  generations  of 

Sediment  affects  giant  kelp  forests 
in  two  other  ways:  large  amounts  of 
shifting  sediment  can  scour  or  bury 
established  populations  in  rocky  areas 
(Weaver  1977),  and  relatively  small 
amounts  of  sediment  on,  or  falling  on,  the 
bottom  can  reduce  the  survivorship  of 
microscopic  life  history  stages.  The 
former  has  been  observed  by  North  (1971b), 
who  suggested  that  Macrocystis  fronds  are 
particularly  susceptible  to  damage  if 
buried,  and  by  Foster  et  al.  (1983),  who 
indicated  that  changes  in  sediment  cover 
may  be  responsible  for  some  of  the  his- 
torical changes  in  the  areal  extent  of 
kelp  forests  in  the  vicinity  of  San 
Onofre.  Johnson  (1980)  recounts  obser- 
vations, made  in  the  late  1800 '  s  on  San 
Miguel  Island  (near  Anacapa  Island,  see 

Chapter  3),  indicating  that  kelp  forests 
were  destroyed  by  sand  eroded  from  the 
land.  Grigg  (1975)  listed  burial  as  an 
important  cause  of  mortality  in  Muricea 
cal ifornica ,  a  gorgonian  coral  commonly 
found  on  reefs  and  in  kelp  forests  south 
of  Point  Conception.  Burial  can  also  kill 
young  hydrocorals  (Allopora  cal ifornica) 
(Ostarello  1973)  and  other  sessile  animals 
(Weaver  1977),  and  may  kill  slow-moving 
invertebrates  like  the  California  cowry 
(SCE  1979).  Sediments  can  clog  the 
filter-feeding  apparatus  of  many  inverte- 
brates, and  may  be  partly  responsible  for 
the  generally  higher  abundances  of  filter 
feeders  such  as  Al lopora  on  vertical 
surfaces  where  sedimentation  is  reduced 
(Ostarello  1973). 

Scour  can  also  be  caused  by  the 
blades  of  understory  algae  rubbing  over 
the  bottom.  Velimirov  and  Griffiths 
(1979)  described  bare  areas  between 
patches  of  Laminaria  pal  1  i da  produced  by 
blades  sweeping  the  bottom.  The  effects 
of  this  type  of  scour  have  not  been 
examined  within  giant  kelp  forests. 

A  mosaic  of  sediment  and  rock  patches 
is  common  in  many  kelp  forests,  and  this 
pattern  may  change,  particularly  during 
storms.  Small  patches  of  shifting  sedi- 
ment are  one  disturbance  that  kills 
established  organisms,  creating  new  space 
for  re-colonization.  This  disturbance  may 
thus  have  important  effects  on  composition 
and  diversity  within  certain  kelp  forests 
(Rosenthal  et  al.  1974,  Foster  1975a, 
Grigg  1975). 

Laboratory  experiments  by  Devinny  and 
Volse  (1978)  showed  that  even  very  small 
amounts  of  sediment  can  greatly  inhibit 
the  attachment  and  growth  of  Macrocystis 
spores.  This  could  have  a  significant 
effect  on  adult  distribution  in  the  field. 
Sedimentation  rates,  as  measured  with 
sediment  tubes,  are  also  negatively 
correlated  with  sporophyte  recruitment 
(Dean  et  al.  1983).  It  is  highly  probable 
that  the  small  stages  of  other  algae  and 
invertebrates  (such  as  gorgonian  corals; 
Grigg  1975)  are  also  negatively  affected 
in  this  way. 

Macrocystis  can  grow  while  drifting, 
and  early  descriptions  of  the  plant  sug- 
gested it  might  exist  in  large  unattached 


floating  masses  as  Sargassum  does  in  the 
Sargasso  Sea  (see  discussion  by  North 
1971b).  Although  "seas"  of  Macrocystis 
have  not  been  found,  Moore  (1943)  and 
Gerard  and  Kirkman  (1984)  described  large 
numbers  of  living  plants  with  unusual 
branched  fronds  drifting  on  the  bottom  in 
quiet  bays  in  southern  New  Zealand. 


Subtidal  organisms  are  continually 
submerged,  and  thus  are  not  exposed  to  the 
extremes  of  temperature  found  in  the 
intertidal  zone.  However,  considerable 
seasonal  and  year-to-year  differences  in 
temperature  occur  within  the  range  of 
giant  kelp  forests.  These  differences 
have  been  suggested  as  important  to  plant 
distribution,  especially  on  a  geographic 
scale  (North  1971b,  Murray  et  al.  1980, 
Van  den  Hoek  1982). 

Any  discussion  of  temperature  (and 
other  abiotic  factors)  must  be  prefaced 
with  warnings  about  factor  covariance  and 
interaction,  relationships  between  tempo- 
ral and  spatial  scales  of  measurement  vs. 
plant  response,  and  differences  in 
response  of  different  life  history  stages 
(see  Wheeler  and  Neushul  1981  for  review). 
The  effects  of  temperature  and  other 
abiotic  factors  are  often  examined  alone 
in  field  correlations  and  single-factor 
laboratory  experiments.  As  pointed  out  by 
Hedgpeth  and  Gonor  (1969),  however,  the 
effects  of  temperature  can  vary  depending 
on  other  factors  such  as  light  and  nutri- 
ents. These  interactions  have  been 
suggested  (Druehl  1978)  or  demonstrated  as 
important  for  Macrocystis  and  other  kelps 
(Luning  and  Neushul  1978,  Dean  et  al . 
1983).  Moreover,  the  measurement  of 
temperature  in  the  field  may  not  truly 
reflect  what  the  organism  actually 
experiences.  For  example,  a  shallow 
thermocline  can  occur  within  kelp  forests, 
with  bottom  temperatures  considerably 
colder  than  those  at  the  surface.  Thus, 
using  surface  temperatures  as  an  indica- 
tion of  temperatures  within  a  kelp  forest 
can  be  inappropriate.  The  vast  majority 
of  seawater  temperature  measurements  are 
made  at  the  surface.  In  addition,  depend- 
ing on  tides,  thermocline  position,  etc., 
temperatures  on  the  bottom  at  kelp  forest 
depths  can  vary  4  c-  8  °C  in  less  than  a 
day    (Quast    1971c,    Barilotti    and 

Silverthorne  1972,  Zimmerman  and  Kremer 
1984).  Rosenthal  et  al.  (1974)  found  mean 
and  maximum  surface  temperatures  near 
their  study  area  over  a  five-year  period 
to  be  16.3  °C  and  24.6  °C,  respectively, 
while  the  mean  at  17  m  was  13.0  °C,  and 
the  maximum  16.0  °C. 

Monthly  mean  surface  temperatures  of 
nearshore  waters  within  the  western  north 
Pacific  distribution  of  large  stands  of 
Macrocystis  pyrifera  vary  from  12  °-  15  °C 
near  Santa  Cruz,  California  to  18  °-  23  °C 
in  Baja  California,  Mexico  (Sverdrup  et 
al.  1942).  It  is  generally  believed  that 
adult  giant  kelp  do  not  grow  well  above  20 
°C,  although  plants  have  been  found  in  an 
area  of  Baja  California,  Mexico,  where 
temperatures  exceeded  this  value  for 
several  weeks  (North  1971b).  This  latter 
observation  may  be  exceptional,  as  plants 
in  Baja  California,  Mexico  generally  occur 
in  areas  where  cool  water  is  upwelled 
(Dawson  1951).  Canopies  and  entire  plants 
deteriorate  in  southern  California  during 
years  when  sea  water  temperatures  are 
elevated  ("El  Nino"  oceanographic  condi- 
tions; see  Section  2.5  below)  suggesting 
that  high  temperatures  (or  associated  low 
nutrients,  see  Section  2.5)  have  deleter- 
ious effects  on  adult  plants. 

Growth  of  gametophytes  of  a  variety 
of  kelp  species  in  southern  California  is 
generally  optimal  at  17  °C,  while  fertili- 
ty is  optimal  at  12  °C.  Both  of  these 
processes  were  optimal  at  around  12  °C  in 
gametophytes  from  central  California 
(Luning  and  Neushul  1978).  Bull  kelp 
(Nereocystis  luetkeana)  does  not  occur 
south  of  Point  Conception,  and  Vadas 
(1972)  concluded  that  this  is  because 
gametophyte  fertility  and  young  sporophyte 
growth  occurred  at  15  °C  but  not  at  20  °C. 
However,  this  conclusion  about  distribu- 
tion is  questionable,  as  temperature 
effects  between  15  °  and  20  °C  were  not 
evaluated,  and  temperatures  below  20  °C 
are  common  for  many  months  of  the  year 
south  of  Point  Conception  (Barilotti  and 
Silverthorne  1972,  Mearns  1978,  Dean  et 
al.  1983).  One  might  expect  that,  if 
temperature  were  of  great  importance  to 
geographic  distribution,  plants  from  areas 
with  different  temperature  characteristics 
would  exhibit  different  responses  to 
temperature.  North  (1972b)  found  that 
sporophytes   transplanted   from   Baja 


California,  Mexico,  to  Newport  Bay  in 
southern  California  survived  better  during 
periods  of  warm  water  than  native  plants. 
Deysher  and  Dean  (pers.  comm. )  are 
evaluating  the  growth  and  fertility  of 
Macrocystis  pyrifera  gametophytes  produced 
from  adults  collected  in  Baja  California, 
Mexico  (warm  water),  the  San  Diego  area 
(moderate-warm  water),  and  Monterey  (cold 
water).  In  contrast  to  the  findings  of 
North  (1972b),  their  preliminary  results 
indicate  all  gametophytes  behave  similar- 
ly, and  sporophyte  production  occurs  at  20 
°C  if  nutrients  are  adequate.  Growth  and 
fertility  decline  rapidly  above  23  °C  in 
all  plants.  More  of  these  kinds  of 
experiments,  combined  with  adequate 
temperature  records  from  geographic  bound- 
aries, are  needed  to  evaluate 
temperature-distribution  hypotheses 
critical ly. 

Temperature  has  also  been  suggested 
as  being  important  to  the  geographic 
distribution  of  kelp  forest  fishes  and 
invertebrates  (Quast  1971a,  Gerrodette 
1979).  As  for  bull  kelp  and  gorgonian 
corals  (see  above),  major  changes  in  the 
distribution  of  kelp  forest  species  occur 
near  Point  Conception  where  the  California 
Current  moves  offshore,  creating  large 
changes  in  temperature  within  a  short 
distance.  Briggs  (1974)  also  emphasized 
the  importance  of  these  changes  near  Point 
Conception  in  his  review  of  marine  bio- 
geography.  However,  most  of  the 
relationships  between  distribution  and 
temperature  are  based  on  correlative 
evidence,  and  the  difficulties  mentioned 
above  for  algal  distribution  also  apply  to 
these  other  kelp  forest  organisms  (see 
Gerrodette  1979). 

2.4.  LIGHT 

The  methods  of  measuring  light 
relative  to  the  biology  of  kelp  forest 
organisms  have  undergone  numerous  changes 
in  recent  years,  and  an  understanding  of 
these  changes  is  necessary  to  interpret 
the  results  of  light  studies.  Luning 
(1981)  recently  reviewed  this  subject,  so 
we  will  only  briefly  summarize  it  here  to 
aid  the  discussion  that  follows. 

Marine  plants  have  a  diverse  array  of 
light-absorbing  pigments  such  that  wave- 

lengths of  between  roughly  400  and  700  nM 
are  used  in  photosynthesis  (so-called  PAR 
or  Photosynthetical  ly  Active  Radiation); 
other  plant  processes  may  be  sensitive  to 
light  outside  this  range  (Luning  1981). 
Inexpensive,  portable  instruments  to 
measure  light  in  this  region  of  the 
spectrum  were  not  available  until 
recently,  and  most  early  measurements  were 
made  with  photometers  that  measure  light 
(illuminance)  in  foot-candles  (English), 
or  lux  (metric;  1  f-c  =  10.764  lux). 
Illuminance  is  based  on  the  sensitivity  of 
the  human  eye,  and  measurement  instruments 
are  designed  with  maximum  sensitivity  in 
the  green  region  of  the  spectrum  (550  nM). 
Therefore,  photometers  do  not  properly 
measure  the  light  actually  available  for 
photosynthesis.  Later  measurements  have 
been  made  with  instruments  that  detect  all 
portions  of  the  spectrum  with  equal 
sensitivity  in  energy  units  (such  as 
watts/m2;  irradiance).  With  proper 
filters,  these  instruments  can  measure 
just  PAR.  Light  quantity  can  also  be 
measured  as  photon  flux  density.  This  is 
a  particularly  appropriate  unit  because 
photosynthesis  is  a  quantum  process. 
Instruments  are  now  available  which 
measure  photon  flux  density  of  PAR.  The 
units  are  Einsteins/area/time  or 
mols/area/time,  where  1  Einstein  =  1  mol  = 
6.02  x  1023  photons.  Unless  otherwise 
noted,  light  measurements  below  are  photon 
flux  density  of  PAR. 

Adequate  light  is  essential  for  the 
growth  of  Macrocystis  and  other  plants 
within  a  kelp  forest,  and  may  affect  the 
behavior  of  other  organisms  such  as  fishes 
(Quast  1971c).  Most  seaweeds  in  a  kelp 
forest  at  least  start  life  on  the  bottom, 
and  light,  as  well  as  other  factors 
affecting  plant  growth,  must  be  suitable 
there.  In  the  absence  of  other  possible 
controlling  factors  (presence  of  sand, 
grazers,  etc.),  the  lower  depth  limit  of 
giant  kelp  and,  therefore,  giant  kelp 
forests,  is  probably  determined  by  light. 
Luning  (1981)  suggested  that  for  most 
kelps,  this  limit  will  occur  where 
irradiance  is  reduced  to  ^  1%  of  that  at 
the  water's  surface.  Giant  kelp  generally 
grows  deeper  in  clearer  water  as  seen  in 
some  central  California  kelp  forests  where 
depth  distributions  are  correlated  with 
water  clarity  (Foster  1982a).  Barilotti 
(pers.   comm.)   notes   that   the   outer 


(deeper)  margin  of  the  Point  Loma  kelp 
forest  has  receded  to  depths  shallower 
than  at  the  turn  of  the  century,  and 
suggested  that  this  may  be  due  in  part  to 
increased  turbidity  associated  with  the 
nearby  San  Diego  sewer  outfall. 

The  quality  or  spectral  distribution 
of  light  also  changes  with  depth  and  water 
characteristics  (Jerlov  1968,  Luning 
1981);  this  may  affect  the  distribution  of 
plants  that  require  particular  wavelengths 
of  light  to  maintain  growth.  In  addition, 
many  kelps  require  a  certain  amount  of 
blue  light  for  the  induction  of  fertility 
in  gametophytes  (Luning  and  Dring  1972, 
Luning  and  Neushul  1978,  Luning  1980). 
For  Macrocystis  at  14  °C,  a  total  of 
between  1.5-12.3  E/m2  of  wavelengths 
between  400  and  530  nM  is  required  to 
induce  50%  fertility  (Luning  and  Neushul 
1978,  Deysher  and  Dean  in  press).  The 
blue  light  response  varies  because  it  is 
affected  by  the  rate  at  which  this  light 
is  received;  gametophytes  have  both 
thresholds  and  saturation  points  (Deysher 
and  Dean  in  press).  Work  with  other  kelps 
suggests  that  the  amount  of  blue  light 
required  also  varies  with  temperature 
(Luning  1980).  Growth  occurs  without  blue 
light,  but  reproduction  does  not. 

Luning's  (1981)  suggestion  that  1%  of 
surface  irradiance  is  required  for  kelp 
growth  is  an  over-simplification  because 
light  requirements  differ  for  different 
stages  of  the  same  plant,  and  these  stages 
occupy  different  depths  and  thus  different 
light  regimes.  The  depth  where  1%  light 
occurs  can  vary  with  water  clarity  and 
canopy  development.  Table  2  lists  light 
requirements  for  growth  in  various  stages 
of  Macrocystis.  The  values  given  should 
be  considered  approximate  as  requirements 
may  vary  with  geographic  location,  temper- 
ature, nutrients  (Luning  and  Neushul 
1978),  water  motion  (Wheeler  1980b)  and, 
for  photosynthetic  measurements  on  adult 
blades,  position  in  the  water  column 
(Wheeler  1980a). 

Growth  will  slow  at  light  levels 
below  saturation,  and  fertility  will 
decline  if  less  blue  light  is  available. 
Dean  et  al.  (1983)  estimated  that 
Macrocystis  gametophytes  outplanted  on 
artificial  substrata  in  the  San  Onofre 
kelp   forest   must   receive   the   light 

Table  2.  Downwelling  light  levels 
(E/m2/day)  for  gametogenesis  and  compen- 
sation (growth)  and  saturation  (highest 
growth  rate)  of  growth  in  various  stages 
of  Macrocystis.  For  reference,  1%  of 
surface  light,  suggested  by  Luning  (1981) 
as  the  lower  light  limit  for  kelp  growth, 
is  about  0.2  E/m2/day. 


Compensation   Saturation 


Growth3     , 

Young  sporophytesc 
(^  1  cm  long) 

0.3        2 

0.2  -  0.4  0.4  -  0. 



Juvenile  sporophytes 
(-X.  0.2-1  m  long)    0.6  -  0.7    2-3 




From  Dean  et  al  .  1983. 

From  Deysher  and  Dean  (in  press). 
.From  Dean  and  Jacobsen  (in  press). 
From  photosynthetic  rates  in  Clendenning 
1971c.  Light  levels  were  converted  from 
foot-candles  using  conversion  of  Luning 
1981,  and  assuming  a  12-h  day  with  con- 
stant light. 

necessary  to  become  fertile  within  about 
40  days.  Beyond  this  time,  mortality  due 
to  factors  such  as  sedimentation  and 
grazing  is  apparently  so  high  that  few 
gametophytes  survive.  This  life  history 
stage  can  live  and  grow  for  much  longer 
periods  in  the  laboratory  (Sanbonsuga  and 
Neushul  1980),  but  whether  gametophytes 
can  live  longer  on  natural  substrata  in 
the  field  is  unknown.  Larger  stages  may 
survive  longer  at  suboptimal  light  levels 
because  they  are  partly  above  the  bottom 
and  not  as  affected  by  these  factors. 

Adult  Macrocystis  plants  are 
generally  insensitive  to  changes  in 
subsurface  light  because  they  usually  form 
a  surface  canopy,  and  can  translocate  the 
products  of  photosynthesis  toward  the 
holdfast  (Parker  1963,  Lobban  1978). 
Younger  stages  are  located  on  or  near  the 
bottom,  however,  so  a  kelp  forest  could 


disappear  even  if  light  was  favorable  for 
adult  growth.  Light  transmission  to  the 
bottom  is  affected  by  the  amount  of 
surface  light,  the  water,  dissolved  and 
suspended  material  in  the  water,  and 
shading  by  attached  organisms.  Surface 
light  intensity  varies  with  latitude, 
season,  and  cloud  and  fog  cover,  but  the 
range  of  intensities  is  much  less  than 
that  created  by  water  characteristics 
(Dean  MS.).  Day  length  may  be  important 
in  triggering  photoperiodic  reactions,  but 
this  has  not  been  investigated  in  subtidal 
plants  (Luning  1981). 

Light  is  attenuated  logarithmically 
with  depth,  and  each  wavelength  has  a 
particular  extinction  coefficient  (Jerlov 
1968).  The  extinction  coefficient  also 
varies  with  turbidity;  in  clear  water, 
blue  light  is  transmitted  further  than 
green  light,  while  in  more  turbid  coastal 
water,  the  reverse  occurs  (Jerlov  1968). 
Overall  light  transmission  declines  with 
increasing  turbidity  and,  within  the 
coastal  water  types  designated  by  Jerlov 
(1968),  Luning  (1981)  estimated  that  the 
depth  where  irradiance  is  reduced  to  1%  of 
surface  varies  between  3  and  30  m. 

Water  clarity  or  turbidity  is 
influenced  by  terrestrial  runoff, 
sediments  resuspended  by  wave  surge  (Quast 
1971c),  plankton  abundance  (Quast  1971c, 
Clendenning  1971b),  and  probably  dissolved 
and  particulate  matter  produced  by  kelp 
forest  organisms  (Clendenning  1971b).  We 
have  observed  the  first  three  of  these  to 
produce  near  darkness  on  the  bottom  in 
kelp  forests  at  mid-day.  Moreover, 
changes  in  water  masses  with  changing 
current  conditions  can  cause  rapid  (less 
than  an  hour)  changes  in  water  clarity. 
For  these  reasons,  short-term  measurements 
of  light  on  the  bottom,  although  useful  in 
comparing  nearby  areas  at  the  same  time, 
should  be  used  with  caution  in 
characterizing  the  light  regime  of  a  site. 
Light  regimes,  particularly  if  they  are  to 
be  used  for  correlations  with  algal 
recruitment  and  growth,  should  be 
determined  with  i_n  situ  continuous 
recorders  (Luning  1981;  see  Ramus  in 
press,  and  Foster  et  al.  in  press  for 

Some  of  the  earliest  observations  in 
kelp  beds  and  forests  suggested  that  the 
plants  themselves  have  a  great  effect  on 
light  reaching  the  bottom  (e.g.,  Kitching 
et  al.  1934).  Macrocystis  canopies  can 
reduce  irradiance  by  over  90%  (Neushul 
1971b,  Dean  et  al.  1983,  Reed  and  Foster 
1984,  Santelices  and  Ojeda  1984a),  and 
dense  surface  canopies  of  giant  kelp  are 
often  associated  with  a  relatively  sparse 
understory  algal  flora  (Dawson  et  al . 
1960,  Neushul  1965,  Foster  1975b).  Within 
a  locality,  understory  algal  cover  (Foster 
1982a)  and  Macrocystis  recruitment 
(Rosenthal  et  al.  1974,  Reed  and  Foster 
1984)  can  vary  inversely  with  Macrocystis 
canopy  cover.  Pearse  and  Hines  (1979) , 
Reed  and  Foster  (1984),  and  Dayton  et  al. 
(1984),  using  experimental  plant  and 
canopy  removals,  have  demonstrated  that 
giant  kelp  canopies  can  inhibit  the 
recruitment  and  growth  of  the  algae 
beneath  them.  Moreover,  natural  kelp 
recruitment  usually  coincides  with  times 
when  the  surface  canopy  is  reduced 
(Rosenthal  et  al.  1974,  Kimura  and  Foster 
in  press).  Santelices  and  Ojeda  (1984b) 
also  report  an  increase  in  Macrocystis 
pyrifera  recruitment  when  the  surface 
canopy  was  experimentally  removed.  In 
contrast  to  some  of  the  above  studies, 
however,  understory  kelp  biomass 

Understory  kelps  such  as  Pterygophora 
cal ifornica,  Eisenia  arborea ,  and 
Laminaria  spp.  cause  further  light 
reductions,  and  the  flora  beneath  stands 
of  _P.  cal ifornica  is  often  reduced  to 
articulated  and  encrusting  corallines 
(Reed  and  Foster  1984).  At  a  constant 
depth  of  15  m,  Reed  and  Foster  (1984) 
measured  photon  flux  densities  of  2%-6%  of 
surface  in  open  water,  0 . 2%-2. 5%  under 
canopies  of  either  Macrocystis  or 
Pterygophora,  and  <  2%  (usually  <~ 0.5%) 
under  their  combined  canopies.  sExperi- 
mental  removal  of  understory  kelp  canopies 
can  result  in  increased  recruitment  and 
growth  of  plants,  including  Macrocystis 
(Kastendiek  1982,  Reed  and  Foster  1984, 
Santelices  and  Ojeda  1984b,  Dayton  et  al . 
1984).  Bottom-cover  plants  such  as 
articulated  corallines  also  inhibit 
recruitment,  at  least  in  part  by  further 
reducing  light  (Reed  and  Foster  1984). 


similar  to 
elements  in 
North  (1980) 



Most  plants,  including  seaweeds,  are 
photoautotrophic;  the  sun  provides  energy, 
but  the  plants  require  a  variety  of 
inorganic  and  some  organic  nutrients,  such 
as  vitamins,  to  manufacture  the  chemicals 
necessary  for  growth  and  reproduction. 
Subtidal  seaweeds  must  obtain  all  their 
nutrients  from  the  water  because  hold- 
fasts are  attached  to  solid  substrata  (no 
soil)  and  appear  to  serve  no  special 
nutrient  uptake  functions.  Moreover, 
except  for  the  occasional  frond  in  the 
surface  canopy,  tissues  are  not  exposed  to 
air,  and  thus  all  metabolic  processes 
occur  in  water. 

Few  macroalgae  have  been  grown  in 
defined  culture  media  in  axenic  condi- 
tions, so  we  know  little  about  their 
complete  nutrient  requirements  (DeBoer 
1981).  The  assumption  is  that  their 
inorganic  requirements  are 
terrestrial  plants  (14-21 
various  forms;  DeBoer  1981). 
identified  38  elements  in 
tissue,  and  Kuwabara  and  North  (1980) , 
using  microscopic  stages  of  M.  pyrifera 
cultured  in  defined  media,  found  that  at 
least  nine  elements  were  essential  for 
growth  and  reproduction.  These,  along 
with  carbon  and  oxygen,  are  listed  in 
Table  3.  DeBoer  (1981)  suggested  that  of 
these,  nitrogen,  phosphorus,  iron,  and 
perhaps  manganese  and  zinc,  may  possibly 
limit  growth  of  macroalgae  in  nature,  and 
North  (1980)  concluded  that  copper  could 
also  be  limiting  for  Macrocystis. 

Of  the  possible  nutrients  that  could 
limit  kelp  forest  algal  growth  in  the 
field,  nitrogen  has  received  the  greatest 
attention,  particularly  as  it  may  affect 
Macrocystis  growth  in  southern  California 
(Jackson  T977,  Wheeler  and  North  1981, 
Gerard  1982a,  b,  c,  Zimmerman  and  Kremer 
1984).  Gerard  (1982a)  indicated  that 
inorganic  nitrogen  concentrations  in  the 
surrounding  water  must  be  in  the  order  of 
1-2  urn  (1pm  =  1  ya -a torn/ liter)  to  support 
a  typical  giant  kelp  growth  rate  of  4% 
increase  in  wet  weight  per  day.  Inorganic 
nitrogen  concentrations  vary  widely  in 
nearshore  waters,  but  are  particularly 
high  during  upwelling  or  when  there  is 
terrestrial  runoff  (North  et  al.  1982). 
They  are  low  (<  lym)  in  summer  and  fall  in 

Table  3.   Known  nutrient  requirements  for 
Macrocystis  pyrifera. 


Form  Normally 
Used  by. 

in  Nature 

Carbon  (C) 

HC03",  C03= 


Oxygen  (0) 



Nitrogen  (N) 

N03-,  NH4+ 


Phosphorus  (P) 



Manganese  (Mn) 



Iron  (Fe) 

coll oidal 


Cobalt  (Co) 



Copper  (Cu) 



Zinc  (Zn) 



Molybdenum  (Mo) 



Iodine  (I) 



j*From  Kuwabara  and  North  1980. 

Where  forms  are  not  given  (--),  it  is 

assumed  that  the  element  is  used  as  a 

free  ion. 
^Frorn  DeBoer  1981. 

May  limit  Macrocystis  growth  in  deep 

oceanic  water  (Kuwabara  1982). 
eToxic  to  Macrocystis  as  free  ions  in 

deep  oceanic  sea  water  (Kuwabara  1982). 

southern  California  (especially  above  the 
thermocline  if  the  water  is  thermally 
stratified),  and  during  periods  when  warm 
water  masses  move  into  the  region  from  the 
south  (Jackson  1977,  Wheeler  and  North 
1981,  North  et  al.  1982).  At  Catalina 
Island  in  southern  California,  daily 
variation  in  nitrate  concentration  is 
frequently  as  great  or  greater  than  mean 
seasonal  variations,  and  at  least  a  one 
day  per  month  intensive  sampling  is  needed 
to  characterize  nitrate  at  this  site 
(Zimmerman  and  Kremer  1984).  Fewer 
measurements  of  inorganic  nitrogen  have 


been  made  in  central  California,  but  those 
available  indicate  levels  are  generally 
above  1  um  in  these  colder  waters  with 
frequent  upwelling  (Gerard  1976,  Broenkow 
and  Smethie  1978). 

In  southern  California,  giant  kelp 
canopies  commonly  deteriorate  during 
summer  when  inorganic  nitrogen  is  low. 
Reduced  nitrogen  concentrations  may  have 
been  responsible  for  the  massive  loss  of 
Macrocystis  during  the  warm-water  period 
of  the  late  1950' s  (North  1971b,  Jackson 
1977,  North  et  al.  1982),  and  plants 
deteriorated  at  many  locations  during  the 
recent  (1982-84)  "El  Nino"  (Dean  pers. 
comm.  ,  Dayton  and  Tegner  1984b).  We  ob- 
served late-summer  canopy  deterioration 
that  may  have  been  due  to  nutrient 
limitation  at  two  locations  in  central 
California  during  1979  and  1982.  However, 
temperature  and  inorganic  nitrogen 
concentrations  are  inversely  correlated 
(Jackson  1977),  so  determining  whether 
inorganic  nitrogen  or  temperature  (or  a 
combination  of  both)  is  responsible  for 
these  phenomena  is  impossible  from 
correlations  alone. 

Evidence  that  low  inorganic  nitrogen, 
not  temperature,  is  limiting  under  low- 
nutrient/high-  temperature  conditions 
comes  from  fertilization  experiments. 
Dean  and  Deysher  (1983)  found  that  more 
sporophytes  were  produced  on  fertilized 
artificial  substrata  inoculated  with  giant 
kelp  spores  and  placed  within  a  kelp 
forest  than  on  similarly  treated  but 
unfertilized  controls.  Zimmerman  (pers. 
comm.)  examined  the  cause  of  the  summer 
decline  in  adult  Macrocystis  growth  at  Big 
Fisherman  Cove  at  Santa  Catalina  Island. 
Summer  growth  was  increased  when  adult 
plants  were  fertilized  with  NaN03. 
However,  growth  was  not  as  great  in  this 
experiment  as  the  highest  natural  growth 
rates  at  other  times  of  the  year, 
suggesting  that  in  summer,  other  nutrients 
and/or  temperature  may  be  limiting  once 
the  nitrogen  requirements  of  the  plants 
are  met.  Laboratory  studies  by  Manley  and 
North  (1984)  suggest  phosphorous  may  be 
particularly  important.  North  (1983b) 
added  nitrate  and  phosphate  to  ambient 
temperature  (18  °-  23  °C)  water  flowing 
into  a  large  tank  containing  adult 
Macrocystis.  These  plants  maintained 
healthy  canopies  and  had  high  tissue 

nitrogen  levels,  while  nearby  plants  in 
the  natural  kelp  forest,  exposed  to 
similar  temperatures  but  not  fertilized, 
suffered  canopy  losses  and  had  low  tissue 

In  addition  to  temperature  (and 
perhaps  other  nutrients),  physiological 
processes  within  giant  kelp  can  further 
obscure  the  relationship  between  nitrogen 
in  the  water  and  plant  growth.  Seaweeds 
can  store  nitrogen  when  the  concentration 
in  the  surrounding  water  is  high  (luxury 
consumption),  and  then  use  these  reserves 
for  growth  when  the  surrounding  concen- 
tration drops  (Chapman  and  Craigie  1977). 
Macrocystis  can  accumulate  non-structural 
nitrogen  compounds  (Wheeler  and  North 
1981,  Gerard  1982b)  including  nitrate 
(Druehl  pers.  comm.),  and  then  use  these 
reserves  to  maintain  growth  for  at  least 
two  weeks  in  low  nitrogen  environments 
(Gerard  1982b).  Thus,  both  the  frequency 
of  environmental  sampling  for  inorganic 
nitrogen  and  the  presence  of  tissue 
reserves  can  affect  the  interpretation  of 
growth  rate  vs.  inorganic  nitrogen  data. 

The  utilization  of  inorganic  nitrogen 
in  the  water  is  also  affected  by  water 
motion  (Gerard  1982c,  Wheeler  1982). 
Increased  water  flow  over  plants  enhances 
uptake  by  increasing  nutrient  transport 
through  the  diffusion  boundary  layer 
(Neushul  1972,  Gerard  1982c).  Gerard 
(1982c)  and  Wheeler  (1982)  found  that 
nitrogen  uptake  by  Macrocystis  increased 
with  increasing  current  speed,  up  to  a 
maximum  at  ^  2-4  cm/sec.  Current 
velocities  in  kelp  forests  are  often  lower 
than  this  (Wheeler  1980b).  However, 
Gerard  (1982c)  has  shown  that  water  flow 
caused  by  wave  surge  can  be  equivalent  to 
that  of  the  current  speeds  above,  and 
pointed  out  that  because  the  plants  are 
attached  to  the  bottom  and  each  blade  is 
attached  to  a  fixed  point  on  the  plant, 
very  small  waves  can  produce  flag-like 
blade  movement.  This  motion,  plus  small 
currents  and  surge,  are  sufficient  to 
saturate  nitrogen  uptake  even  under  very 
calm  conditions. 

Little  information  is 

available  on 

possible  nutrient  limitations  in  other 
kelps  in  giant  kelp  forests.  Work  in 
eastern  Canada  (Chapman  and  Craigie  1977, 
Gagne  et  al.  1982)  and  the  Arctic  (Chapman 


and  Lindley  1980)  indicated  that  seasonal 
and  site  differences  in  kelp  (Laminaria 
spp.)  growth  in  these  regions  are  related 
to  the  availability  of  inorganic  nitrogen. 
The  only  other  giant  kelp  forest  plant  so 
far  investigated  that  may  be  nutrient- 
limited  in  the  field  is  Gel idium  robustum 
(formerly  G.  cartilagineum) ,  an  agar- 
producing  red  alga  (see  Chapter  4).  Tseng 
and  Sweeney  (1946)  determined  that  this 
plant  u=ses  dissolved  C02  rather  than  HC03" 


or  CO, 

The  plant  is  most  abundant  at 

wave-exposed  sites  in  shallow  water  (<  12 
m)  where  dissolved  C02  is  more  common. 
This  suggests  that  carbon  availability  may 
limit  the  distribution  both  within  (with 
depth)  and  between  (exposed  vs.  sheltered) 
sites.  Barilotti  (1980)  indicated  that 
light  and  grazing  may  also  affect  G. 
robustum  distribution. 


Currents  and  surge  produced  by  wind, 
tides,  or  waves  have  numerous  direct  and 
indirect  effects  on  kelp  forest  communi- 
ties. Currents  are  unidirectional  flows 
(but  the  direction  can  change  within 
hours),  while  surge  moves  back  and  forth 
over  the  bottom,  as  well  as  up  and  down 
above  the  bottom  (Figure  4).  Current 
speeds  in  kelp  forests  are  highly 
variable,  but  in  the  range  of  near  0  to  15 
cm/sec  in  the  few  kelp  forests  studied 
(Wheeler  1980b,  Bray  1981,  Jackson  1983). 
Neushul  et  al .  (1967)  measured  speeds  of 
40  cm/sec  near  Anacapa  Island.  The  drag 
at  higher  speeds  can  pull  Macrocystis  over 
at  angles  up  to  30  degrees  from  vertical, 
and  the  entire  surface  canopy  may  submerge 
as  a  result  (Neushul  et  al.  1967).  This 
canopy  submergence,  along  with  that  caused 
by  changes  in  tide,  can  alter  canopy 
extent  as  estimated  with  aerial 
photographs.  As  a  result  of  plant  drag, 
current  speeds  within  kelp  forests  are 
often  two  to  three  times  lower  than  the 
surrounding  water  (Jackson  and  Winant 
1983),  and  if  the  forest  is  small,  the 
incoming  current  will  diverge  around  it, 
producing  a  "bow  wake"  similar  to  that  of 
a  ship  (Jackson  1983).  The  reduction  of 
surface  waves  by  kelp  plants  is  commonly 
observed  as  "quiet  water"  inshore  from 
kelp  forests  (Darwin  1860),  and 
artificial,  kelp-like  tethered  floats  have 
been  used  as  breakwaters  to  reduce  water 
movement  in  harbors  (Isaacs  1976). 

Figure  4.  Water  motion  produced  by  swells 
in  shallow  water.  Note  that  the  orbital 
motion  of  water  particles  flattens  toward 
the  bottom,  eventually  becoming  entirely 
horizontal  to  produce  surge.  In  the 
example  shown,  a  5-m  excursion  of  water 
was  measured  on  the  bottom  at  a  depth  of 
6  m,  when  a  2-m  wave  moved  past  at  a 
velocity  (C)  of  8  m/sec,  a  wave  length  (L) 
of  120  m,  and  a  wave  period  (T)  of  15  sec. 
Orbital  velocities  at  the  surface  are  also 
shown  (re-drawn  from  Neushul  1972). 

Even  at  high  speeds,  currents  have 
not  been  observed  to  cause  mortality  of 
adult  kelp  forest  organisms.  They  do, 
however,  indirectly  affect  nutrient  uptake 
by  plants  (see  2.5  above),  larval  and 
spore  dispersal  within  and  between  kelp 
forests,  and  the  distribution  of  particles 
that  may  serve  as  food  for  benthic  animals 
(Pequegnat  1964)  and  fish  (Bray  1981). 

Surge  speeds  can  be  much  higher  than 
currents,  particularly  surge  generated  by 
long  period  swells  associated  with  winter 
or  tropical  storms.  In  central 
California,  4-m  high  swells  are  typical  in 
winter  and  produce  water  speeds  of  over  1 
m/sec  on  the  bottom  at  kelp  forest  depths 
(10  m).  The  force  generated  by  water 
moving  this  fast  is  equivalent  to  the 
force  produced  by  a  wind  speed  of  126  mph 
(56  m/sec;  Charters  et  al.  1969).  As 
noted  above  (Section  2.2),  such  forces  can 
pull  benthic  organisms  off  the  bottom  and 
fracture  the  bottom  in  the  process. 
Storm-associated  surge  is  perhaps  the  most 
important  source  of  mortality  for  adult 
Macrocystis  in  California  (ZoBell  1971, 
Rosenthal  et  al.  1974,  Gerard  1976,  Foster 
1982a,  Reed  and  Foster  1984,  Dayton  et  al . 
1984)  and  at  sites  studied  in  Argentina 
(Barrales  and  Lobban  1975).   Plants  are 


often  torn  loose  in  patches 
when  one  loose  individual  e 
others  still  attached.  This 
drag  on  the  holdfasts  of 
plants,   contributing   to 
detachment  (Rosenthal  et  al 
the  substratum  is  very  hard 
firmly  attached,  surge  may 
long  fronds,  leaving  the 
small  fronds  that  may  grow 
(Foster  1982a). 

during  storms 
ntangles  with 
increases  the 
the  attached 
.  1974).  If 
and  holdfasts 

remove  only 
holdfast  and 

vegetati vely 

Differences  in  swell  exposure 
probably  account  for  many  of  the 
differences  in  canopy  and  plant  density 
fluctuations  between  southern  and  central 
California.  The  east-west  trend  in  the 
coastline,  protection  provided  by  offshore 
islands,  and  the  distance  from  the 
northerly  source  of  most  winter  storms  all 
combine  to  make  many  southern  California 
kelp  forests  relatively  protected  from 
large  swells.  Surface  canopies  in  this 
region  typically  vary  in  extent  in  a 
three-  to  four-year  cycle  (North  1971b, 
Rosenthal  et  al.  1974),  probably  related 
to  an  increased  susceptibility  of  older 
and  larger  plants  with  deteriorating 
holdfasts  to  removal  by  water  motion. 
Canopies  around  Santa  Barbara  are  even 
less  variable,  with  occasional 
catastrophic  losses  due  to  atypically 
large  swells  (Ebeling  et  al.  MS.)  or  warm 
water  (low  nutrient)  periods  (North 
1971b).  There  are  exceptions,  however; 
large  swells  in  winter  1982-83  removed 
nearly  70%  of  the  adult  Macrocystis  at 
some  sites  in  the  Point  Loma  kelp  forest 
near  San  Diego  (Dayton  and  Tegner  1984b), 
and  over  90%  of  the  Macrocystis  surface 
canopy  along  the  Palos  Verdes  Peninsula, 
Los  Angeles  (Wilson  and  Togstad  1983). 

In  contrast,  most  canopies  in  central 
California  undergo  a  regular  seasonal 
change  with  growth  in  spring  and  summer 
leading  to  maximum  development  in  early 
fall,  and  then  frond  and  plant  loss  during 
late  fall  and  winter  storms  (Miller  and 
Geibel  1973,  Cowen  et  al.  1982,  Foster 
1982a,  Kimura  and  Foster  in  press).  In 
addition  to  these  seasonal  changes,  there 
are  year-to-year  differences  correlated 
with  the  severity  of  winter  swells  (Foster 
1982a).  This  was  especially  evident  in 
winter  1982-83,  when  swells  over  7  m  high 
with  a  21-sec  period  were  recorded  in 
central  California  (Seymour  1983).   Large 

swells  along  the  entire  California  coast 
during  this  period  removed  almost  all 
Macrocystis  surface  canopies  (McPeak  pers. 
comm. ). 

If  swells  are  too  extreme, 
Macrocystis  may  not  be  able  to  persist  in 
a  given  area.  In  the  absence  of  biotic 
factors  such  as  competition  (Santelices 
and  Ojeda  1984b),  swells  may  determine  the 
shoreward  depth  limit  of  kelp  forests 
(North  1971b)  because,  for  a  given  set  of 
swell  characteristics,  surge  speed 
increases  as  depth  decreases.  On  a 
geographic  scale,  increasing  surge  may  be 
the  primary  reason  why  M.  pyrifera  does 
not  occur  in  large  stands  north  of  Ano 
Nuevo  Island  (near  Santa  Cruz)  in  central 
California.  Nereocystis  luetkeana  is 
extremely  resistant  to  breakage  from  water 
drag  (Koehl  and  Wainwright  1977),  and  is 
the  common  canopy-forming  kelp  from  Ano 
Nuevo  Island  north  into  Alaska.  This 
change  in  surface  canopy  species  may  also 
be  related  to  differences  in  life  history 
characteristics,  growth  rates,  and 
susceptibility  to  grazing  (see  Chapters  3 
and  4). 

Understory  kelps  seem  generally  more 
resistant  to  removal  by  surge  (Reed  and 
Foster  1984,  Dayton  et  al.  1984),  but 
these  kelps,  along  with  foliose  algae  that 
cover  the  bottom,  may  also  be  directly 
removed  by  surge,  particularly  if  the 
substratum  is  soft  rock  (Foster  1982a). 

Swells  can  also  alter  fish 
distribution  (Quast  1971c),  and  can  remove 
attached  or  mobile  benthic  invertebrates, 
especially  those  that  project  into  the 
water  above  the  bottom.  Hines  (1982) 
suggested  that  winter  swells  may  be  an 
important  source  of  mortality  in  kelp 
forest  spider  crab  populations.  Cowen  et 
al.  (1982)  found  that  sea  urchin 
(Stongylocentrotus  franciscanus)  behavior 
was  modified  during  winter  when  storms 
apparently  caused  animals  to  clump  in 
cracks  and  depressions,  and  Agegian  et  al . 
(in  prep.)  suggest  that  mortality  caused 
by  surge  at  some  sites  in  central 
California  may  restrict  S_.  franciscanus 
distribution  to  deeper  water  or  to  areas 
protected  from  high  water  motion  in 
shallow  water.  The  white  urchin, 
Lytechinus  anamesus,  moves  less,  covers 
itself  with  debris,  and  even  burrows  into 


shell  debris  during  periods  of  surge  (Lees 
and  Carter  1972).  Activity  of  the  sea 
urchin  Centrostephanus  coronatus  is  also 
reduced  in  turbulent  conditions,  and 
Lissner  (1980)  suggested  that  this  urchin 
may  also  be  excluded  from  areas  by  high 
water  motion.  Because  sea  urchin  grazing 
can  significantly  alter  the  distribution 
of  other  kelp  forest  organisms  (see 
Chapter  3),  the  effects  of  water  motion  on 
sea  urchin  distribution  and  activity  can 
have  significant  indirect  effects  on 
community  structure. 

In  addition  to  affecting  distribution 
and  behavior,  water  motion  may  alter  the 
orientation  of  sessile  organisms.  The 
plane  of  the  primary  dichotomy  of 
Macrocystis  (Neushul  et  al.  1967),  the 
branches  of  gorgonians,  and  the  understory 
kelp  Eisenia  arborea  (Foster  pers.  obs.) 
are  commonly  oriented  perpendicular  to  the 
most  common  swell  direction,  presumably  an 
adaptation  to  reduce  mortality  due  to 
water  motion  and/or  to  increase  capture  of 
nutrients  or  planktonic  food.  Other 
characteristics  of  seaweed  morphology 
related  to  water  motion  are  discussed  by 
Neushul  (1972). 

Water  motion  has  numerous  indirect 
effects  on  kelp  forests,  and  some  of 
these,  such  as  nutrient  uptake  and  changes 
in  turbidity,  scour,  and  sedimentation, 
are  discussed  with  other  abiotic  factors. 
Of  particular  importance  are  effects  on 
light  caused  by  removal  of  overstory 
canopies  during  storms.  In  exposed  kelp 
forests  in  central  California,  increased 
light  resulting  from  the  removal  of  Macro- 
cystis canopies  by  storms  is  correlated 
with  a  three-fold  or  more  increase  in  the 
cover  of  understory  plants  (Foster  1982a). 
Moreover,  if  understory  kelps  are  sparse, 
giant  kelp  removal  can  affect  kelp 
recruitment  as  well  (Rosenthal  et  al. 
1974,  Pearse  and  Hines  1979,  Reed  and 
Foster  1984).  Many  of  the  direct  and 
indirect  effects  of  water  motion  are 
illustrated  in  the  community  regulation 
models  shown  in  Figure  5.  These  models 
illustrate  that  the  relative  importance  of 
particular  factors  can  vary  among  kelp 

forests,  that  factors  are  often 
correlated,  and  how  they  can  interact  to 
affect  the  species  composition  and 
distribution  of  organisms. 











CLEAR   WATER -"Macrocystis  >30m  DEEP 


— '  Pterygophora  MORTALITY    LOWj   , 








l-SOFT  ROCK    5 
—  LOW 


TURBID  WATER  — Macrocystis. 12m  DEEP 


Pterygophora  MORTALITY   HIGH 






=  Primary  factors 

=  Factor  interactions 

=  Regulatory  pathways  (how  factors  affect 

Figure  5.  Factors,  factor  interactions, 
and  regulatory  pathways  affecting  the 
algal  associations  in  two  giant  kelp 
forests  in  central  California  (see  Chapter 
3;  from  Foster  1982a). 



The  biotic  components  and  temporal  population  changes 
recorded  off  Del  Mar  should  not  be  interpreted  as  "charateristic" 
of  all  southern  California  kelp  beds.  Rosenthal  et  al.  (1974). 


We  have  defined  giant  kelp  forests  as 
subtidal  communities  composed  of  Macro- 
cystis  pyrifera  and  associated  organisms. 
Although  by  definition,  Macrocystis  is 
always  present  in  these  communities,  its 
local  distribution  and  abundance  vary  in 
time  and  space,  as  do  the  distribution  and 
abundance  of  other  plants  and  animals 
associated  with  it  (Clarke  and  Neushul 
1967,  Rosenthal  et  al.  1974,  Foster 
1982a).  In  addition,  within  the 
geographic  range  of  Macrocystis  forests, 
the  species  composition  of  associated 
organisms  can  also  vary;  their  geographic 
ranges  are  not  necessarily  the  same  as  for 
Macrocystis.  So  far  as  is  known,  no 
organisms  found  in  stands  of  giant  kelp 
have  an  obligate  association  with 
Macrocystis;  they  can  be  found  in  other 
kelp  communities  and  on  subtidal  rocky 
reefs  devoid  of  large  brown  algae 
(Pequegnat  1964,  see  Chapter  4).  In  this 
chapter  we  describe  the  community 
structure  of  a  number  of  sites,  discuss 
the  spatial  and  temporal  variability  of 
this  structure,  and  review  kelp  forest 

To  aid  the  discussion  that  follows, 
Figure  6  illustrates  a  "composite"  giant 
kelp  community  with  emphasis  on  the  large, 
visually  obvious  kelps  that  provide  much 
of  the  structure  of  the  community,  and  for 
which  we  have  the  most  descriptive 
information.  The  figure  divides  the 
community  into  habitats  within  giant  kelp 

forests  where  particular  organisms  typi- 
cally co-occur.  It  is  a  composite,  both 
because  of  local  variation  in  species 
distribution,  and  because  the  geographic 
ranges  of  some  of  the  organisms,  such  as 
sea  otters  (Enhydra  lutris)  and  the  elk 
kelp  (Pelagophycus  porra) ,  do  not 
presently  overlap.  The  figure  does,  how- 
ever, indicate  the  potential  complexity  of 
the  community,  with  multiple  layers  of 
vegetation  (Dawson  et  al.  1960,  Foster 
1975a),  over  50  species  of  fishes  that 
commonly  segregate  into  various 
microhabitats  (Quast  1971a,  Miller  and 
Geibel  1973,  Feder  et  al.  1974,  Ebeling  et 
al.  1980a),  and  numerous  invertebrates 
also  found  in  particular  habitats  (e.g., 
on  plants,  on  vertical  or  horizontal 
surfaces,  and  on  holdfasts).  North 
(1971b)  listed  130  species  of  plants  and 
almost  800  species  of  animals  associated 
with  giant  kelp  in  southern  California  and 
northern  Baja  California,  Mexico.  The 
giant  kelp  holdfast  alone  may  contain  over 
150  species  (Ghelardi  1971).  A  variety  of 
birds  and  mammals  forage  in  the  community, 
including  cormorants,  harbor  seals,  and 
sea  otters.  Kelp  forests  also  contain  a 
planktonic  assemblage  of  generally 
microscopic  organisms,  many  of  which  are 
stages  in  the  life  histories  of  larger 
members  of  the  community. 

As  indicated  in  Figures  3,  6,  9,  and 
10,  Macrocystis  communities  generally 
occur  within  a  narrow  depth  range.  Even 
if  suitable  substrata  are  available,  M. 
pyrifera  usually  does  not  occur  shallower 


than  %  5  m,  and  deeper  than  about  20  m. 
Depending  on  location,  other  kelps  may 
form  relatively  sparse  surface  canopies  in 
shallower  or  deeper  water.  These  areas 
outside  the  range  of  Macrocystis  are  also 

included  in  the  discussion  below,  as 
organisms  within  a  kelp  forest  may  have 
ranges  that  extend  both  shallower  and 
deeper  than  Macrocystis. 


i€  ® 







Figure  6.  Cross-section  showing  the  inhabitants  of  a  generalized  giant  kelp  forest. 
The  numbers  to  the  right  indicate  vegetation  layers  (see  legend  for  Figure  3).  Three 
broad  zonal  associations  along  the  depth  gradient  are  shown:  Zl,  inshore  of  the  giant 
kelp  community;  12,  within  the  giant  kelp  community;  and  Z3,  offshore  from  the  giant 
kelp  community.  Various  subcommunities  or  associations  are  indicated  by  the  circular 
diagrams:  A,  animals  associated  with  the  surface  of  Macrocystis  and  other  seaweeds 
(polychaetes ,  isopods,  bryozoans);  B,  plankton  in  the  water  (various  phytoplankton, 
zooplankton  and  larval  fish);  C,  animals  found  in  giant  kelp  holdfasts  (small  sea 
urchins,  brittle  stars,  crustaceans,  polychaetes;  although  shown  on  the  outside,  these 
organisms  occupy  the  spaces  between  the  haptera);  D,  plants  and  animals  characteristic 
of  horizontal  surfaces  (various  sea  stars,  urchins,  benthic  fishes,  understory  algae); 
E,  organisms  most  common  on  vertical  surfaces  (primarily  sessile  animals  such  as 
sponges,  tunicates,  bryozoans  and  sea  anemones).  Some  of  the  organisms  shown  do  not 
co-occur  at  any  one  site  (from  Foster  et  al .  1983). 



3.2.1  Giant  Kelp  Forests 

Stands  of  Macrocystis  pyrifera  occur 
as  far  north  as  Ano  Nuevo  Island,  approxi- 
mately 30  km  north  of  Santa  Cruz  in 
central  California  (North  1971b,  Druehl 
1970;  Foster  pers.  obs. ;  Figure  7).  The 
species  does  not  occur  in  Oregon  (Phinney 
1977)  or  British  Columbia  (Scagel  1967). 
Stands  can  occur  as  far  south  as  Punta 
Asuncion-Punta  San  Hipolito  in  Baja 
California,   Mexico  (27°N  lat. ;   Dawson 

1951,  North  1971b),  but  this  southern 
limit  varies.  Estes  (pers.  comm. ) 
reported  that  as  of  the  summer  of  1984, 
the  most  southerly  plants  were  around  the 
San  Benito  Islands,  over  240  km  north-west 
of  Punta  Asuncion-Punta  San  Hipolito.  This 
probably  reflects  the  effects  of  storms 
and  changes  in  water  characteristics 
associated  with  the  recent  "El  Nino"  (see 
Chapter  3).  In  California,  giant  kelp 
canopies  occupy  an  area  of  about  110 
km2(Miller  and  Geibel  1973),  although  this 
is  highly  variable  between  seasons  and 
years  (see  Section  3.5). 

Figure  7.     The  distribution  of  algae  that  form  surface  canopies  in  the  northeast 
Pacific  (redrawn  from  Druehl  1970). 


3.2.2  Other  Kelp  Forests 

Bull  kelp,  Nereocystis  luetkeana 
(Figure  3),  occurs  from  near  Point 
Conception,  California,  to  the  eastern 
Aleutian  Islands,  Alaska  (Druehl  1970), 
and  is  the  most  abundant  surface  canopy 
kelp  in  California  north  of  Santa  Cruz 
(Figure  7).  Where  its  range  overlaps  with 
Macrocystis  pyrifera,  the  two  plants  can 
occur  both  in  separate  and  mixed  stands 
(Yell  in  et  al.  1977).  Another  kelp, 
A! aria  fistulosa,  can  also  form  surface 
canopies  in  Alaska  (Druehl  1970,  Dayton 
1975).  Macrocystis  integrifol ia ,  a  low 
intertidal-shallow  subtidal  species,  has  a 
range  similar  to  that  of  the  bull  kelp 
(Druehl  [1970]  indicates  Monterey  as  its 
southern  limit),  and  may  form  thick 
canopies  in  shallow,  protected  water  (<  8 
m  deep;  Scagel  1967).  Egregia  menziesii 
(Figure  3),  the  feather  boa  kelp,  occurs 
from  Baja  California,  Mexico  to  British 
Columbia  (Druehl  1970,  Abbott  and 
Hollenberg  1976),  and  often  forms  a  sparse 
canopy  inshore  from  stands  of  M.  pyrifera. 

There  are  no  surface  canopy  kelps  in 
the  eastern  north  Pacific  south  of  the 
range  of  Macrocystis  pyrifera.  Members  of 
the  fucalean  (Phylum  Phaeophyta,  Order 
Fucales)  genus  Sargassum  may  form  surface 
canopies  in  the  shallow  waters  of  the  Gulf 
of  Mexico  and  the  Gulf  of  California. 
Species  of  Sargassum,  especially  the 
recently  introduced  S_.  muticum  (Ambrose 
and  Nelson  1982,  Deysher  and  Norton  1982), 
may  also  form  surface  canopies  in  shallow 
water  in  British  Columbia-Washington 
(Norton  1981,  DeWreede  1983),  and  in 
southern  California,  particularly  in 
protected  areas  around  Catalina  Island 
(Ambrose  and  Nelson  1982).  Cystoseira 
osmundacea  (Figure  3),  a  native  fucalean, 
occurs  from  Ensenada,  Baja  California  to 
Oregon  (Abbott  and  Hollenberg  1976).  This 
plant  has  a  perennial  vegetative  base  that 
produces  long,  floating,  reproductive 
fronds  in  spring  and  summer.  Cystoseira 
can  occur  as  pure  stands  in  shallow  water, 
and  mixes  with  other  surface  canopies  in 
deeper  water.  It  is 
as  deep  as  kelps, 
usually  occur  at  the 

Pacific  is  the  elk  kelp,  Pelagophycus 
porra  (Figure  3).  This  huge  plant 
generally  does  not  reach  the  surface;  its 
long,  wide  blades  stream  out  in  currents 
just  beneath  the  surface  or,  in  areas 
around  Catalina  Island,  California,  drape 
over  the  bottom.  Plants  are  most  common 
along  the  outer  margins  of  Macrocystis 
forests  around  the  southern  Channel 
Islands  and  other  southern  California 
islands,  and  along  the  mainland  from  the 
San  Benito  Islands  in  Baja  California  to 
San  Diego  (Dawson  et  al.  1960,  Abbott  and 
Hollenberg  1976).  These  geographic 
distributions  are  summarized  in  Figure  7. 


The  greatest  difficulty  in  describing 
giant  kelp  forest  communities  is  that  only 
a  few  sites  have  been  studied  in  detail, 
and  as  pointed  out  in  Chapter  1, 
quantitative  information  on  abundances 
versus  depth  is  lacking.  Thus,  many  of 
the  generalizations  about  community 
structure  and  the  processes  that  affect  it 
are,  at  present,  preliminary,  and  should 
be  viewed  with  caution. 

Given  the  complexity  of  kelp 
communities  and  the  qualitative  nature  of 
most  descriptive  data,  we  have  chosen  to 
illustrate  kelp  forest  variability  by 
describing  a  few  sites  that  have  been 
studied  in  some  detail.  Ten  sites  (Figure 
8)  are  examined  in  Sections  3.3.1  and 

Greyhound  Rock' 
Sondhill  Bluff 


generally  not  found 

and  mixed  canopies 

inner  edge  of  kelp 


The  only  other  kelp  that  can  form  a     Figure  8.    Location  of  the 
surface   canopy   in   the   eastern   north     forests  described  in  Chapter  3. 

ten  kelp 


3.3.2,  five  in  central  California  (Figure 
9),  and  five  in  southern  California 
(Figure     10).       Community     composition     in 

other  geographic  areas  is  discussed  in 
Section  3.3.3.  It  is  impossible  to 
discuss     completely     the     large    number    of 

Greyhound  Rock 


Bottom  Cover  Algae 

Botryogloaaum  farlowianum 

Polyneura  latissima 

Deamareatia  ligulata  20m 

8»89ile  Animals 



Sandhill  Bluff 

Bottom  Cover  Algae 
Foliose  Red  Algae 
(as  at  Greyhound  Rock) 

Sessile  Animals 





Point  Cabrillo 

Stillwater  Cove 

Bottom  Cover  Algae 

Glgartlna  corymblfera 
Rhodymenia  spp. 
Sessile  Animals 
Solitary  Corals 


Bottom  Cover  Algae 

Calliarthron  cheiloaporloldes 
Plocamlum  cartilaglneum 

Sessile  Animals  30m 


Granite  Creek 

Laminaria  dentigera 


Egregia  menziesii 

Nereocystis  luetkeana 


Bottom  Cover  Algae 

Calliarthron  cheilosponoides 
Plocamium  cartilagineum 

Ova       Macro 


cystis  pynfere 

Cystoseira  osmundacea 
Phyllospadix  spp. 

Patina  miniata 
^  ^     Pisaster  giganteus 



Red  &  Purple  sea  urchins 

Pholad  clams 
Diopatra  ornata 


Bottom  Cover  Algae 

Sessile   Animals 



Figure  9.   The  distribution  of  conspicuous  plants  and  animals  found  in  five  central 
California  kelp  forests.   Horizontal  axes  are  not  to  scale. 


species  that  can  occur  in  each  kelp 
forest,  so  we  will  concentrate  on  the 
distribution  of  large,  abundant  organisms. 

Details  of  the  natural  history  of  these 
plants  and  animals  can  be  found  in  Chapter 
4.  A  discussion  of  variation  within  sites 

Figure  10.   The  distribution  of  conspicuous  plants  and  animals  found  in  five  southern 
California  kelp  forests.  Horizontal  axes  are  not  to  scale. 


follows  the  site  descriptions  (Section 
3.4),  and  Chapter  5  examines  in  detail 
current  hypotheses  about  the  causes  of 
variation  within  and  among  sites. 

3.3.1  Central  California  Greyhound  Rock.  The  site  is 
located  25  km  north  of  Santa  Cruz,  and  4 
km  south  of  Ano  Nuevo  Island  (Figure  8), 
the  northern  limit  of  large  stands  of 
Macrocystis  pyrifera.  Although  a  few 
small  stands  of  Macrocystis  occur  to  the 
north,  Greyhound  Rock  is  presently  a 
Nereocystis  luetkeana  forest  (Figure  9). 
It  has  been  surveyed  a  number  of  times 
since  1976  (Yell  in  et  al.  1977,  Foster  et 
al.  1979a,  b,  Foster  and  Reed  1980, 
Foster  and  Heine  1981,  Foster  1982a). 

The  substratum  is  composed  of 
mudstone  ridges  interspersed  with  sand 
that  terminate  in  a  large  sand  plain  at 
^  20-m  depth.  The  site  is  fully  exposed 
to  northwest  swells  and  the  water  is 
generally  turbid.  At  depths  of  5-8  m 
inshore  of  the  Nereocystis  forest, 
the  rocky  ridges  are  covered  with  multiple 
layers  of  foliose  vegetation  (especially 
the  red  algae  Botryoglossum  farlowianum, 
Polyneura  latissima,  and  Phycodrys 
setchel li  i ,  and  the  brown  Desmarestia 
1 igulata  var.  1 igulata) ,  along  with 
scattered  patches  of  the  understory  kelps 
Dictyoneurum  cal i form' cum  and  Laminaria 
setchel 1 ii  [L.  dentigera  in  Abbott  and 
Hollenberg  1976,  but  see  Druehl  1979). 
The  vertical  sides  of  the  ridges  are 
covered  with  various  tunicates  and 
sponges,  and  the  few  red  sea  urchins 
(Strongylocentrotus  franciscanus )  present 
occur  on  the  sides  of  ridges  facing  shore. 

Nereocystis  occurs  on  the  tops  of 
ridges  at  depths  of  8-14  m.  Beneath  it 
are  sparse  stands  of  the  understory  kelps 
Laminaria  setchel 1 ii  and  Pterygophora 
cal ifornica,  with  foliose  algae  beneath. 
The  walls  and  ledges  beneath  the  ridgetops 
are  dominated  by  red  sea  urchins, 
encrusting  coralline  algae,  sponges, 
tunicates,  sea  anemones,  and  solitary 
corals.  Predatory  sea  stars  (Pycnopodia 
hel  ianthoides ,  Pisaster  brevispinus,  _P_. 
giganteus,  and  _P.  ochraceous)  are  common, 
as  is  the  omnivorous  bat  star  Patiria 

Large,  foliose  algae  are  rare  seaward 
of  the  Nereocystis  stand  (below  14  m),  and 
the  substratum  is  dominated  by  encrusting 
coralline  algae,  barnacles  (Balanus 
crenatus) ,  sea  anemones  (Corynactis 
cal ifornica) ,  red  sea  urchins,  and  sea 
stars  (especial ly  Pisaster  spp.).  Fishes 
at  this  site  have  not  been  studied.  Sandhill  Bluff.  This  site 
is  a  Macrocystis  pyrifera  forest  located 
10  km  south  of  Greyhound  Rock  (Figure  8). 
The  area  is  described  in  the  literature 
cited  under  Greyhound  Rock  above  and  in 
Cowen  et  al .  (1982).  The  rocky  substratum 
is  relatively  flat  mudstone  interspersed 
with  sand  patches  (Figure  9).  In  deeper 
water  (14  to  17  m)  beyond  the  kelp  forest, 
rock  terminates  in  an  entirely  sand 
bottom.  The  kelp  forest  is  in  the  lee  of 
a  small  point,  and  is  thus 
slightly  protected  from  northwest  swells. 

Macrocystis  pyrifera  forms  a  surface 
canopy  at  depths  between  6  and  14  m 
(Figure  9).  Along  the  inshore  edge  of  the 
forest  where  giant  kelp  is  absent,  the 
bottom  is  dominated  by  foliose  red  algal 
species  similar  to  those  at  Greyhound  Rock 
but,  at  this  site,  these  plants  grow  over 
dense  mats  of  bryozoans,  sponges,  and 
tunicates.  Where  a  surface  canopy  is 
present,  the  algal  understory  is  reduced. 
Small  Pterygophora  cal ifornica  and 
Laminaria  setchel 1 ii  occur  in  widely- 
dispersed  patches.  Factors  affecting  the 
algal  assemblage  at  this  site  are  shown  in 
Figure  5. 

Understory  algal  cover  is  reduced 
beneath  the  Macrocystis  canopy.  Sponges, 
tunicates,  and  pholad  clams  are  common, 
but  over  50%  of  the  substratum  can  be 
unoccupied  rock.  Red  sea  urchin  abundance 
is  low  (<  1/m2),  and  individuals  are 
clumped  in  small  crevices  and  depressions. 
The  sea  stars  Patiria  miniata,  Pycnopodia 
hel ianthoides  and  Pisaster  spp.  are 

Offshore  from  the  giant  kelp  canopy, 

foliose  red  algal  cover  is  greater  and 

understory  kelps  are  less  abundant.  The 

tube   polychaete   Diopatra   ornata ,  the 

anemone   Corynactis   cal ifornica,  and 

compound  tunicates  cover  much  of  the 

substratum.   Sea  stars  found  under  the 

canopy  are   common  offshore,   and  the 


abundance  of  red  sea  urchins  increases  to 
over  1/m2.  Striped  surfperch,  Embiotoca 
lateralis,  are  abundant  at  this  site 
(Cowen  1979),  but  other  fishes  have  not 
been  studied. 

We  noted  an  increase  in  sea  otter 
abundance  and  a  decline  in  red  sea  urchins 
at  both  Sandhill  Bluff  and  Greyhound  Rock 
during  qualitative  surveys  in  August, 
1983.  Whether  this  decline  was  associated 
with  the  severe  storms  in  winter  1982-83, 
sea  otter  foraging,  or  some  other  cause  is 
unknown.  Point  Cabrillo  kelp  forest. 
This  forest,  located  in  southern  Monterey 
Bay  off  Hopkins  Marine  Station  in  Pacific 
Grove  (Figure  8),  has  been  extensively 
studied  (Lowry  and  Pearse  1973,  Miller  and 
Geibel  1973,  Devinny  and  Kirkwood  1974, 
Pearse  and  Lowry  1974,  Lowry  et  al.  1974, 
Harrold  1981,  Riedman  et  al.  1981,  Breda 
1982,  Hines  1982,  Hines  and  Pearse  1982, 
Fadlallah  1983,  Watanabe  1983,  1984a,  b). 
Seventy-seven  species  of  algae,  292 
species  of  invertebrates,  59  species  of 
fishes,  and  various  birds  and  mammals 
including  the  sea  otter  and  herbor  seals 
occur  at  Point  Cabrillo  (Miller  and  Geibel 
1973,  Pearse  and  Lowry  1974).  The  surface 
canopy  is  Macrocystis  pyrifera  and 
Cystoseira  osmundacea  that  grows  attached 
to  large  granite  outcrops  and  boulders  in 
an  area  very  protected  from  swells  (Figure 

Here,  Macrocystis  grows  in  very  shal- 
low water  (~  3  m).  Extensive  beds  of  surf 
grass,  Phyl lospadix  spp.  ,  patches  of  the 
feather  boa  kelp  Egregia  menziesi  i ,  and 
in  summer,  dense  masses  of  the  floating 
reproductive  fronds  of  Cystoseira 
osmundacea  occur  inshore  of  the  giant 
kelp;  C.  osmundacea  also  occurs 
intermixed  with  Macrocystis  out  to  14  m 
(Schiel  in  press  a).  Beyond  14  m,  the 
rock  is  replaced  by  sand,  with  abundant 
tube-dwelling  polychaetes  (Diopatra 
ornata),  and  sea  anemones  (Pachycerianthus 

The  kelp  Dictyoneuropsis  reticulata 
forms  a  sparse  understory  beneath  the 
surface  canopy,  and  the  bottom  is 
dominated  by  the  foliose  red  algae 
Gigartina  corymbifera,  Rhodymenia  spp., 
Botryocladia   pseudodichot.oma,   Prionitis 

lanceolata  and  encrusting  corallines. 
Sponges,  tunicates,  anemones,  bryozoans, 
hydroids,  and  solitary  corals  are  common, 
particularly  on  the  sides  of  rocks. 
Spider  crabs  occupy  a  number  of  different 
subhabitats  in  the  forest  (Hines  1982), 
and  various  turban  snails  (Tegula  spp., 
Cal  liostoma  spp.)  are  abundant,  especially 
on  the  algae  (Lowry  et  al.  1974).  Red  and 
purple  sea  urchins  and  abalone  (Haliotis 
rufescens  and  H_.  walal  lensis)  are  common 
in  crevices  (Lowry  and  Pearse  1973).  A 
variety  of  sea  stars  is  found  in  this  kelp 
forest  (Harrold  1981),  with  Patiria 
miniata  most  abundant.  Miller  and  Geibel 
(1973)  described  the  fishes  at  Point 
Cabrillo  in  1969  and  1970.  The  most 
abundant  were  juvenile  rockfish,  followed 
by  adult  blue  rockfish.  Other  common 
species  included  kelp  bass;  striped,  pile, 
black,  and  rainbow  surfperch;  kelp 
rockfish;  greenling;  and  senorita.  Stillwater  Cove.  This  stand 
of  giant  kelp  is  located  inside  Carmel  Bay 
about  5  km  south  of  Monterey  (Figure  8). 
The  site  has  been  described  by  Andrews 
(1945),  Foster  et  al.  (1979a,  b),  Foster 
(1982a),  and  Reed  and  Foster  (1984).  It 
faces  south  and  is  thus  protected  from 
northwest  swells.  The  conglomerate  and 
sandstone  bottom  is  a  mosaic  of  plateaus 
and  pinnacles  surrounded  by  relatively 
flat  rock  or  fields  of  small  boulders. 
One  stand  of  Macrocystis  inteqri folia 
occurs  from  the  lower  intertidal  to  a 
depth  of  ~  1  m  (Figure  9).  Both 
Cystoseira  osmundacea  and  Egregia 
menziesi i  occur  with  M.  integri folia  and 
seaward  into  the  M.  pyrifera  forest.  The 
understory  kelp  Laminaria  setchellii 
occurs  in  patches  down  to  ~  7  m,  and 
bottom  cover  plants  in  shallow  water 
include  the  brown  alga  Dictyota 
binghamiae,  the  articulated  corallines 
Calliarthron  chei losporoides  and  C. 
tuberculosum,  and  encrusting  corallines. 

Macrocystis  pyrifera  occurs  at  depths 
between  2  and  30  m,  terminating  at  a  sand 
bottom  in  deep  water.  Beneath  the 
Macrocystis  are  dense  stands  of  the  under- 
story kelp  Pterygophora  cal ifornica. 
These  plants  are  large  (over  1  m  tall), 
and  particularly  abundant  on  the  tops  of 
plateaus  (Reed  and  Foster  1984). 
Articulated   (Calliarthron   tuberculosum, 


Bossiella  cal ifornica  ssp.  schmitti )  and 
encrusting  corallines  cover  most  of  the 
flat  substratum  beneath  these  Pterygophora 
stands.  There  are  occasional  spring- 
summer  blooms  of  benthic  diatoms  and  the 
fleshy  red  algae  Botryoglossum 
farlowianum,  Plocamium  cartilagineum,  and 
Laurencia  subopposita,  all  commonly 
epiphytic  on  the  articulated  corallines. 
Sessile  animals  are  again  most  abundant  on 
vertical  and  sloping  substrata,  with 
bryozoans,  sponges,  solitary  corals,  and 
sea  anemones  being  the  most  common. 
Factors  affecting  the  algal  assemblage  are 
shown  in  Figure  5. 

As  at  Point  Cabrillo,  grazing 
gastropods  of  the  genus  Tegula  are 
extremely  abundant,  especially  on 
Macrocystis  pyrifera.  Small  (1-2  cm) 
purple  sea  urchins  (Strongylocentrotus 
purpuratus)  are  common  in  the  articulated 
coralline  understory.  Large  urchins  and 
abalone  are  rare,  perhaps  because  this 
site  lacks  suitable  cracks  and  crevices 
that  serve  as  refuges  from  sea  otter 
predation.  The  lined  chiton  Tonicel la 
1 ineata  is  abundant  on  encrusting 
corallines.  Patiria  miniata  is  very 
abundant,  but  the  densities  of  other  stars 
are  reduced  relative  to  the  sites 
discussed  above. 

Qualitative  observations  of  fish  have 
been  made  at  this  site  since  1976  by 
students  at  Moss  Landing  Marine 
Laboratories.  The  most  abundant  groups 
are  juvenile  rockfish,  adult  blue  and  kelp 
rockfishes,  various  surf perches,  and 
greenlings.  Black-eyed  gobies  and 
sculpins  are  common  on  the  bottom.  Granite  Creek.  The  species 
composition  and  distribution  of  algae  and 
invertebrates  at  this  site  south  of 
Monterey  (Figure  8)  were  studied  by  McLean 
(1962)  between  1959  and  1961.  At  this 
time,  the  most  abundant  canopy  kelp  was 
Nereocystis  luetkeana,  growing  on  an 
irregular  granite  bottom  fully  exposed  to 
swells.  Both  Macrocystis  and  Nereocystis 
have  occurred  at  the  site  since  1961 
(Foster  pers.  obs. ). 

In  1959-61,  Egregia  menziesii , 
Cystoseira  osmundacea,  and  Macrocystis 
pyrifera  formed  a  mixed  canopy  inshore 
(0-10  m  depth)  of  Nereocystis.  The  bottom 

in  this  area  was  almost  completely  covered 
by  the  articulated  (Cal 1 iarthron 
chei losporioides)  and  encrusting 
corallines,  with  occasional  patches  of 
Laminaria  setchellii  (Figure  9). 

Nereocystis  grew  attached  to  the 
irregular  substratum  between  10  and  20  m. 
Rock  was  replaced  by  sand  in  deeper  water. 
The  understory  beneath  the  bull  kelp  was 
dominated  by  dense  stands  of  large 
Pterygophora  cal ifornica.  Other 
understory  species  included  the  kelp, 
Costaria  costata,  other  brown  algae 
(Desmarestia  1  igulata  var.  1 igulata, 
Egregia  menziesii ,  Cystoseira  osmundacea, 
and  Dictyota  binghamiae)  and~the  red  alga 
Plocamium  cartilagineum.  These  algae 
were  particularly  abundant  on  the  tops  of 
boulders  where  Pterygophora  cover  was 

McLean  (1962)  lists  32  common 
invertebrate  species  on  vertical  walls  in 
the  kelp  forest,  and  13  on  horizontal 
surfaces  under  the  Pterygophora  canopy. 
Chitons  (Cryptochiton  stelleri ,  Tonicel la 
1  ineata)  and  the  turban  snail  Tegula 
brunnea  were  common,  as  were  Patiria 
miniata  and  Pycnopodia  hel  ianthoides. 
When  surveyed,  this  area  had  recently  been 
foraged  by  sea  otters,  and  large  red  sea 
urchins  were  absent.  Fishes  have  not  been 
studied  here. 

3.3.2  Southern  California  Campus  Point,  Goleta.  This 
site  is  located  at  the  northwest  end  of 
Goleta  Bay  approximately  16  km  northwest 
of  Santa  Barbara  (Figure  8).  The 
description  below  is  based  on  Neushul  et 
al .  (1976)  and  Foster  (pers.  obs.). 

Like  most  of  the  mainland  coast  near 
Santa  Barbara,  Campus  Point  is  protected 
from  swells  by  Point  Conception  to  the 
north,  and  the  Channel  Islands  to  the 
southwest.  The  bottom  is  low  relief 
mudstone  interspersed  with  extensive  sandy 
areas  and  occasional  rocky  outcrops. 
Macrocystis  pyrifera  {M.  angustifol ia  in 
Neushul  et  aT  [1976];  see  discussion  in 
Chapter  1)  occurs  between  depths  of  5  and 
20  m.  At  its  inner  edge,  the  kelp  forest 
is  bounded  by  patches  of  the  feather  boa 
kelp  Egregia  menziesi i ,  and  the  bottom 
cover  is  composed  of  the  red  algae 


Coral lina 



aspergil lum  (articulated  coral  lines) , 
Chondria  nidifica,  Cryptopleura  violacea, 
and  the  brown,  Zonaria  farlowii"  (Figure 
10).  These  plants  commonly  grow  over  a 
turf  of  Pterosiphonia  dendroidea  and  other 
small  red  algae;  all  are  frequently 
covered  by  sand,  and  the  vegetation  is 
best  developed  on  slightly  elevated  rocks. 

Pterygophora  californica  is  the  most 
common  understory  alga  within  the  giant 
kelp  forest,  growing  in  dense  stands 
separated  by  extensive  sandy  areas. 
Fleshy  red  algae  (primarily  Callophyllis 
spp.  ,  Cryptopleura  violacea  and 
Stenogramme  interrupta)  are  sparse  on 
exposed  rocks  and  on  the  tubes  of  the 
polychaete  Diopatra  ornata.  Much  of  the 
hard  bottom  is  bare  or  occupied  by 
rock-boring  pholad  clams.  The  whelk 
Kelletia  kelletii  and  sea  stars  (Pisaster 


"Patiria  '  miniata,  Dermasterias 
imbricata)  are  common,  and  red  and  purple 
sea  urchins  are  abundant  on  isolated  rock 

Extensive  areas  of  deep  sand  occur 
along  the  seaward  border  of  the  forest. 
Fishes  have  not  been  surveyed.  Anacapa  Island.  In  contrast 
to  the  mainland,  waters  around  the  Channel 
Islands  are  generally  clearer,  high-relief 
rock  is  more  common  and,  as  discussed  by 
Murray  et  al.  (1980),  there  is  greater 
spatial  variability  in  temperature.  The 
first  two  conditions  are  particularly 
favorable  to  the  growth  of  giant  kelp  and 
other  rocky  subtidal  organisms.  Qualita- 
tive comparisons  indicate  that  the  diver- 
sity of  kelp-forest  organisms  is  high  on 
the  islands  relative  to  the  mainland. 
Ebeling  et  al.  (1980a)  suggested  that  the 
continuity  of  wel 1 -developed  rocky  reefs, 
clearer  water,  and  the  high  density  of 
algal  and  invertebrate  turf  (an  important 
source  of  fish  food)  on  the  islands  also 
contribute  to  increased  density,  biomass, 
and  diversity  of  fish  there  versus  the 
mainland.  The  discussion  below  is  based 
on  Neushul  et  al.  (1967)  and  Clarke  and 
Neushul  (1967),  who  surveyed  a  700-m  long 
mixed  sand-rock  transect  through  a  giant 
kelp  forest  at  Anacapa  Island  (Figure  8) 
from  0  to  40-m  depth  (Figure  10). 

These  investigators  recognized  three 
broad  zones  along  the  transect.  The  first 

was  a  shallow  zone  from  0  to  8  m  with 
abundant  understory  kelps  (Eisenia 
arborea,  Laminaria  farlowii ) ,  surfgrass 
(Phyl lospadix  torreyJTJ  and  sea  anemones 
(Anthopleura  xanthogrammica) .  Below  this 
was  a  wide,  mid-depth  zone  (8-34  m)  of 
Macrocystis  pyrifera  growing  over  the 
understory  kelps  Agarum  fimbriatum  and 
Pterygophora  californica.  Common  animals 
here  included  "  sea  urchins 
(Strongyl  ocentrotus  franciscanus,  S^. 
purpuratus,  Lytechinus  anamesus),  and  bat 
stars  (Patiria  miniata).  Macrocystis  did 
not  occur  below  34  m;  the  final  zone  in 
deeper  water  was  inhabited  by  A. 
fimbriatum  and  a  variety  of  small  red 
algae.  Fishes  were  not  surveyed,  but  off 
Santa  Cruz  Island  to  the  west,  such 
species  as  the  senorita,  kelp  perch,  giant 
kelpfish,  blacksmith,  and  blue  rockfish 
were  common  in  midwater,  while  the 
California  sheephead,  opaleye,  halfmoon, 
kelp  bass,  kelp  rockfish,  and  various 
surf perches  were  common,  both  in  midwater 
and  on  the  bottom.  Various  rockfishes  and 
gobies  are  common  on  the  bottom  (Ebeling 
et  al.  1980a). 

Santa  Catalina  Island. 


relatively  warm  waters  of  the  kelp  forests 
at  Santa  Catalina  Island  (Figure  8),  like 
Del  Mar  and  Point  Loma  below,  contain 
species  not  found  in  the  more  northern 
areas  described  above.  Among  the  more 
conspicuous  of  these  are  elk  kelp 
Pelagophycus  porra,  the  sea  urchin 
Centrostephanus  coronatus,  and  the 
blue-banded  goby  Lythrypnus  dal 1 i. 
Dykzeul  and  Given  (1979)  reviewed  the 
various  marine  and  terrestrial  habitats 
around  the  western  end  of  Santa  Catalina 
Island;  the  information  below  is 
summarized  from  their  discussion  of 
subtidal  boulder  habitats  near  Big 
Fisherman's  Cove  and  from  our  personal 

The  shallow  subtidal  zone  east  of  Big 
Fisherman's  Cove  (Figure  10)  is  composed 
of  metamorphic  (schist)  boulders  of 
varying  size  that  terminate  in  a  sand 
plain  at  around  35  m.  At  depths  of  0-8  m, 
the  bottom  is  dominated  by  the  understory 
kelp  Eisenia  arborea.  The  brown  algae 
Cystoseira  neglecta,  Dictyota 
flabellulata,  and  Pachydictyon  coriaceum 
are  common  on  the  bottom,  as  are  the  reds 
Lithothrix  aspergillum,  Plocamium  sp. ,  and 


Pterocladia  capillacea.  Common  inverte- 
brates include  red  sea  urchins 
(Strongylocentrotus  franciscanus ) ,  keyhole 
limpets  (Megathura  crenulata) ,  "and  spiny 
lobster  (Panulirus  interruptus) . 
Conspicuous  fishes  include  the  opaleye, 
garibaldi,  blacksmith,  and  topsmelt. 

Macrocystis  pyrifera  occurs  from 
^8-20  m.  The  understory  beneath  its 
surface  canopy  is  relatively  reduced, 
with  patches  of  Cystoseira  neglecta, 
Sargassum  muticum,  Dictyota  f label lulata, 
Pachydictyon  coriaceum  and  various  species 
of  the  red  alga  Gel  idium,  particularly 
where  the  surface  canopy  is  thin  or 
absent.  Much  of  the  bottom  is  covered  by 
encrusting  coralline  algae.  Invertebrates 
include  those  in  shallow  water  plus  the 
additional  sea  urchin  Centrostephanus 
coronatus,  Octopus  bimaculatus,  sea  stars 
(Pisaster  spp. ) ,  and  the  whelk  Kelletia 
kel letii .  The  grazing  gastropod  Norrisia 
norrisi  is  common  on  Macrocystis.  Fishes 
such  as  the  senorita,  kelp  perch,  and 
blacksmith  are  common  in  mid-water  and  the 
Macrocystis  surface  canopy,  while 
California  sheephead,  rock  wrasse, 
senorita,  various  surfperch,  and  gobies 
are  abundant  on  and  just  above  the  bottom. 

In  deeper  water  outside  the  giant 
kelp  canopy,  the  understory  is  again 
dominated  by  the  kelp  Eisenia  arborea ,  as 
well  as  Agarum  fimbriatum  and  Laminaria 
farlowii .  The  browns  Zonaria  farlowii  and 
Dictyopteris  undulata ,  encrusting  and 
articulated  corallines,  and  the  red  algal 
epiphyte  Acrosorium  uncinatum  are  present 
around  and  beneath  the  understory  kelp 
canopy.  The  common  benthic  invertebrates 
in  the  deep  area  are  sea  urchins 
(Centrostephanus  coronatus) ,  sea  stars 
(Henricia  leviuscula,  Linckia  columbiae, 
Pisaster  giganteusj,  snails  (NorrisTa 
norrisi ,  Tegula  aureotincta) ,  and  various 
bryozoans.  Black-eyed  gobies  are  abundant 
on  the  bottom,  while  halfmoon,  garibaldi, 
California  sheephead,  and  senorita  are 
common  just  above  the  bottom  and  in  mid- 
water.  Del  Mar.  Rosenthal  et  al. 
(1974)  made  extensive  observations  of  the 
organisms  in  a  small  kelp  stand  off  Del 
Mar  (Figure  8)  approximately  25  km  north 
of  San  Diego.  This  study,  done  between 
1967  and  1973,  is  the  most  thorough,  long- 

term  natural  history  study  published  on  a 
kelp  forest.  Community  composition  is 
summarized  below,  and  temporal  patterns 
will  be  discussed  in  Section  3.4. 

Like  many  mainland  southern 
California  giant  kelp  forests,  the  stand 
at  Del  Mar  is  isolated  by  a  surrounding 
sand  bottom.  Plants  in  the  stand  occur  on 
a  mixed  sandstone  and  siltstone  bottom, 
with  large  areas  of  sand  and  silt  among 
the  rock.  The  depth  of  this  low  relief 
area  is  between  14  and  20  m.  As  in  the 
other  areas  described  above,  the 
understory  vegetation  beneath  the  Macro- 
cystis pyrifera  was  relatively  sparse, 
with  only  occasional  individuals  of 
Pterygophora  cal ifornica  and 
Laminaria  farlowi  i ,  and  a  few  foliose 
brown  (Desmarestia  1 igulata  var. 
ligulata)  and  Feci  [Rhodymenia  pacifica) 
algae.  Most  of  the  bottom  was  covered 
with  encrusting  corallines  (Figure  10). 

Ninety-eight  species  of  epibenthic 
invertebrates  were  identified  by  Rosenthal 
et  al .  (1974)  in  the  kelp  forest,  the  most 
common  larger  species  being  the  tube 
polychaete  Diopatra  ornata,  the  solitary 
tunicate  Styela  montereyensis,  the 
gorgonian  Muricea  cal ifornica,  the  whelk 
Kelletia  kel letii ,  and  the  rock  boring 
clam  Parapholas  cal ifornica.  Pisaster 
giganteus  was  the  most  conspicuous  sea 
star.  Both  red  and  purple  sea  urchins 
were  present,  though  not  abundant,  and 
were  largely  restricted  to  rock  mounds  and 
boulders  as  they  are  at  Campus  Point 
(described  above). 

Thirty-eight  species  of  fishes  were 
observed,  and  included  most  of  those 
common  on  reefs  and  in  kelp  forests  in 
southern  California  (see  Chapter  4, 
Section  4.5).  Point  Loma.  The  Point  Loma 
kelp  forest  is  located  along  the  western 
shore  of  Point  Loma  between  the  entrance 
of  Mission  Bay  and  San  Diego  Bay  (Figure 
8).  This  kelp  forest  was  %  11  km  long  and 
1  km  wide  in  1977  (Bernstein  and  Jung 
1979),  but  has  varied  greatly  in  extent 
since  the  early  1900' s  (North  1969,  Dayton 
et  al.  1984).  It  was  extensively  surveyed 
by  Turner  et  al.  (1968)  to  detect  possible 
effects  of  the  San  Diego  sewer  outfall. 
Given  such  a  large  area,  one  might  expect 


considerable  spatial  variation  within  the 
forest,  as  is  evident  from  a  comparison  of 
the  four  transects  surveyed  by  Turner  et 
al .  (1968).  This  spatial  variation  will 
be  discussed  in  Section  3.4.  Below  we 
describe  an  idealized  transect  (Figure 
10),  summarizing  and  combining  the  data 
from  all  the  transects  surveyed.  Surveys 
have  also  been  done  in  the  nearby  kelp 
forest  at  La  Jolla  (Aleem  1956,  1973; 
Neushul  1965),  but  are  not  discussed  here. 

The  kelp  forest  occurs  on  a  broad, 
gently-sloping  mudstone-sandstone  terrace 
with  pockets  of  sand,  cobbles  and 
boulders.  Macrocystis  pyrifera  was  most 
abundant  between  6  and  25  m  on  rocky 
substrata.  Inshore  of  the  giant  kelp 
forest,  the  surf  grass  Phyl lospadix 
torreyi  was  particularly  abundant,  along 
with  the  surface  canopy  brown  algae 
Egregia  menziesii  and  Cystoseira 
osmundacea.  Articulated  corallines  were 
also  common,  as  were  black  perch  and 

When  Turner  et  al .  (1968)  studied 
Point  Loma,  giant  kelp  was  sparse, 
particularly  on  the  more  northerly 
transects.  Understory  kelps  were  patchy 
in  occurrence  but  common,  with 
Pterygophora  cal ifornica  most  abundant. 
Common  bottom  cover  algae  included 
articulated  corallines  and  Rhodymenia  spp. 
The  sea  anemone  Corynactis  cal ifornica, 
the  solitary  coral  Balanophyllia  eiegans, 
the  solitary  tunicate  Styela 
montereyensis,  and  various  sponges  were 
the  most  common  sessile  animals.  The 
whelk  Kel letia  kel leti i ,  bat  stars,  and 
red  and  white  sea  urchins  were  the  more 
common  mobile  invertebrates.  Red  urchins 
appeared  to  be  keeping  some  areas  clear  of 
foliose  macroalgae.  The  most  common  fish 
within  the  kelp  forest  were  blacksmith, 
senorita,  California  sheephead,  kelp  bass, 
and  the  black-eyed  goby. 

The  terrace  sloped  more  steeply 
beyond  25  m  depth,  and  in  this  deep  region 
outside  the  giant  kelp  canopy  or 
occasionally  mixed  with  it,  occurred  the 
elk  kelp  Pelagophycus  porra.  Beneath  were 
sparse  stands  of  Laminaria  farlowii,  and  a 
reduced  bottom  cover  of  articulated 
corallines,  Rhodymenia  spp.  and  Plocamium 
cartilagineum.  Invertebrates  here  were 
similar  to,  but  less  diverse  than,  those 

at  the  outer  edge  of  the  giant  kelp 
forest;  the  gorgonian  Lophogorgia 
chi lensis  was  particularly  abundant.  Red 
urchins  were  absent.  The  fishes,  like  the 
invertebrates,  were  generally  similar  to 
those  found  within  the  giant  kelp  forest. 

3.3.3  Other  Geographic  Areas 

With  the  exception  of  a  number  of 
recent  papers  on  South  American  kelp 
forests,  little  information  is  available 
on  subtidal  Macrocystis  communities  in 
other  parts  of  the  world.  Kuhnemann 
(1970)  described  the  vertical  structure  of 
the  vegetation  in  kelp  forests  in  southern 
Argentina.  Canopy  layering  is  similar  to 
forests  in  California  but,  with  the 
exception  of  Macrocystis  pyrifera ,  the 
species  composition  is  very  different. 
Barrales  and  Lobban  (1975)  surveyed  seven 
sites  on  the  coast  of  Argentina  in  March 
1974,  and  found  M^.  pyrifera  to  occur  from 
the  low  intertidal  to  a  depth  of  15  m. 
Plants  were  excluded  from  deeper  water  by 
lack  of  hard  substrata.  The  species 
composition  of  associated  organisms  varied 
with  exposure  to  oceanic  swells.  Barrales 
and  Lobban  (1975)  suggested  that 
Macrocystis  in  this  region  goes  through  a 
three-  to  four-year  loss-replacement  cycle 
caused  by  holdfast  deterioration  and 
storms.  Older  holdfasts  are  apparently 
weakened  by  a  boring  isopod  (Phycol imnoria 
sp.)  and  become  susceptible  to  removal  by 
surge  after  three  to  four  years  of  growth. 
These  authors  also  suggested  that  this 
regular  loss-replacement  cycle  contributes 
to  the  low  species  diversity  of  these 
forests  relative  to  those  in  California. 
However,  some  forests  in  California  can 
exhibit  similar  cycles  (see  Section 
3.5.1).  Sea  urchins  were  not  abundant  at 
these  South  American  sites,  and  appeared 
to  have  little  impact  on  the  community. 

Giant  kelp  forests  in  southern  Chile 
are  also  apparently  limited  to  shallow 
water  by  lack  of  suitable  substrata,  and 
their  inner  margins  can  be  determined  by 
competition  with  understory  kelps 
(Santelices  and  Ojeda  1984b).  These 
authors  suggested  that  the  Macrocystis 
pyrifera  loss-replacement  cycle  described 
by  Barrales  and  Lobban  (1975)  in  Argentina 
does  not  occur  at  their  site.  Two  species 
of  the  kelp,  Lessonia ,  form  understory 
canopies  in  southern  Chile,  and  foliose 


red  algae  are  common  on  the  bottom. 
Experiments  by  Castilla  and  Moreno  (1982) 
indicated  that  the  four  species  of  sea 
urchins  inhabiting  this  area  feed  on  drift 
algae  and  have  little  impact  on 
Macrocystis  recruitment,  growth,  or 
survivorship.  The  Macrocystis  holdfast 
fauna  is  less  diverse  than  that  in 
California  (Ojeda  and  Santelices  1984),  as 
are  the  fish  associated  with  the  forest 
(Moreno  and  Jara  1984). 

More  northerly  Chilean  kelp  forests 
studied  by  Moreno  and  Sutherland  (1982) 
are  also  often  limited  to  shallow  water  by 
lack  of  hard  substrata,  and  giant  kelp 
abundance  is  regulated  primarily  by  water 
motion  and  not  herbivorous  urchins  or 
mol luscs. 

3.4.1  Between  Depths 

Although  considerable  variation  in 
distribution  with  depth  exists  both 
between  and  within  sites  (see  Section  3.3; 
Turner  et  al .  1968),  a  general  pattern  of 
algal  distribution  emerges  from  the 
California  sites  above.  If  rocky 
substratum  is  available  from  the  low 
intertidal  to  depths  where  light  is 
insufficient  for  macroalgal  growth,  three 
subtidal  zones  can  be  recognized,  similar 
to  those  proposed  by  Neushul  (1965;  Figure 

Zone  1,  inshore  of  Macrocystis,  is 
commonly  inhabited  by  Phyllospadix  spp. 
(surf  grass),  feather  boa  kelp  (Tgregia 
menziesii) ,  and  Cystoseira  osmundacea. 
Depending  on  geographic  location  and 
exposure  to  swell,  Eisenia  arborea, 
Pterygophora  cal ifornica,  Laminaria  spp. , 
various  species  of  Sargassum,  and 
articulated  corallines  may  be  present. 
Macrocystis  is  most  abundant  in  Zone  2, 
may  be  mixed  with  C.  osmundacea  throughout 
California,  and  may  be  mixed  with,  or 
replaced  by,  Nereocystis  luetkeana  in 
central  California.  Various  understory 
kelps  (particularly  _P.  cal  ifornica  and  J.. 
farlowii )  occur  in  patches  under 
Macrocystis,  and  articulated  (especially 
Calliarthron  spp.)  and  encrusting 
corallines  are  most  common  on  the  bottom. 
Zone  3,  seaward  of  the  Macrocystis  canopy, 
may  be  inhabited  by  Pelagophycus  porra  in 

southern  California,  or  more  commonly  by 
sparse  stands  of  understory  kelps  such  as 
Agarum  fimbriatum  and  JL.  farlowii , 
encrusting  corallines,  and  small  foliose 
red  algae. 

Invertebrate  zonation  is  not  as 
distinct,  although  broad  changes  along  a 
depth  gradient  in  the  distribution  of  sea 
urchins  have  been  noted  (purple  urchins  in 
shallow  water,  red  urchins  at  mid-depths, 
and  in  southern  California,  white  urchins 
and  Centrostephanus  coronatus  in  deeper 
water).  But  there  are  numerous  excep- 
tions: e.g.,  Sandhill  Bluff  above,  and 
other  areas  where  red  urchins  are  most 
abundant  at  the  outer  edge  of  giant  kelp 
distribution  (Yellin  et  al .  1977,  Pearse 
and  Hines  1979).  Three  common  species  of 
turban  snails  (Tegula)  in  central 
California  also  occur  in  different  depth 
zones  subtidally:  T.  brunnea  at  0-6  m,  T. 
montereyi  at  3-9  m,  T.  poll  i  go  at  7-12  m 
(Riedman  et  al .  1981,  Watanabe  1984a). 
In  general,  sessile  invertebrate  abundance 
increases  with  depth  (Aleem  1973),  perhaps 
in  part  due  to  reduced  competition  for 
space  with  algae  (Foster  1975b). 

The  distribution  and  abundance  of 
fish  species  are  often  not  clearly  zoned 
along  a  depth  gradient.  Distribution 
appears  most  strongly  related  to  vertical 
relief,  including  that  due  to  vegetation, 
rather  than  depth  (Quast  1971a,  Ebeling  et 
al.  1980a,  Moreno  and  Jara  1984,  Larson 
and  DeMartini  in  press;  see  Section  4.5). 
Within  continuous  reef  habitats,  however, 
closely  related  species  may  segregate  with 
depth  (Hixon  1980,  Larson  1980a). 

3.4.2  Within  Depths 

Few  published  surveys  discuss  the 
distributional  variation  of  plants  or 
animals  within  depths,  but  qualitative 
observations  and  the  high  variances 
associated  with  abundance  estimates  at  any 
particular  depth  (Rosenthal  et  al.  1974, 
Foster  et  al .  1979a,  Pearse  and  Hines 
1979)  suggest  that  distributions  are 
generally  clumped  at  fairly  small  scales. 
This  variability  can  result  from  a  number 
of  processes,  including  variability  in 
distribution  of  many  abiotic  factors 
discussed  in  Chapter  2,  as  well  as 
environmental   changes   created   by   the 


organisms  themselves,  particularly  by  the 
large  kelps.  Kelps  in  dense  stands  can 
effectively  exclude  many  other  algae  (Reed 
and  Foster  1984,  Dayton  et  al.  1984). 
Moreover,  the  dispersal  range  of  many 
large  kelps  is  probably  only  several 
meters  from  attached  adults  (Anderson  and 
North  1966,  Schiel  1981)  contributing  to 
the  maintenance  of  local  stands. 
Dispersal  distances  for  invertebrates  can 
also  be  quite  short  (Ostarello  1976, 
Gerrodette  1981).  Inhibition  of 
settlement  by  established  sessile 
organisms  (Breitburg  1984),  local  grazing 
by  sea  urchins  (Turner  et  al.  1968,  Vance 
1979,  Cowen  et  al.  1982,  Dean  et  al.  1984, 
Harrold  and  Reed  in  press)  predator-prey 
interactions  (Bernstein  and  Jung  1979, 
Schmitt  1982),  territorial  behavior  and 
competitive  interactions  among  fish 
(Clarke  1970,  Hixon  1980,  Larson  1980a), 
physical  disturbance  (Cowen  et  al.  1982, 
Wells  1983)  and  competition  among  algae 
(Kastendiek  1982,  Reed  and  Foster  1984, 
Dayton  et  al.  1984)  also  contribute  to 
variations  in  distribution.  Stochastic 
events  are  probably  also  important,  but 
detailed  descriptions  necessary  to  detect 
them  have  not  been  done.  However,  in 
these  diverse  and  structurally  complex 
communities,  most  of  the  patterns  of 
within-depth  distribution  remain 
undescribed,  and  the  mechanisms  creating 
these  patterns  are  unknown  --  a  fruitful 
area  for  further  research. 


3.5.1  Long-Term  (>  5  years) 

The  best  records  of  long-term  (>  5 
years)  changes  in  California  kelp  forests 
come  from  maps  of  kelp  canopy  distribu- 
tion, the  first  of  which  were  made  in 
1910,  1911,  and  1912  (McFarland  1912, 
Crandall  1915).  Comparisons  with  recent 
surveys  indicate  an  overall  30%-70% 
decline  in  the  area  of  giant  kelp  canopies 
in  southern  California  since  these  early 
surveys  (Hodder  and  Mel  1978,  Neushul 
1981).  Hodder  and  Mel  (1978),  however, 
suggested  that  the  magnitude  of  the 
decline  may  be,  in  part,  an  artifact  of 
differences  in  canopy-mapping  techniques. 
Sewage  pollution  (Leighton  et  al .  1966, 

Grigg  and  Kiwala  1970,  Wilson  1982, 
Meistrell  and  Montagne  1983),  abnormal 
oceanographic  conditions  ("El  Nino"  years: 
warm  water,  low  nutrients;  Jackson  1977), 
and  sea  urchin  grazing  (Leighton  et  al. 
1966,  North  1974)  stimulated  by  sewage 
(North  1974)  and/or  removal  of  sea  urchin 
predators  by  man  (North  1974,  Tegner  and 
Dayton  1981)  have  all  been  implicated  as 
causative  agents.  As  these  factors  may 
all  affect  canopy  distribution,  and 
because  information  about  organisms  in  the 
community  other  than  Macrocystis  and 
Nereocystis  is  almost  non-existent  prior 
to  the  1950's,  we  will  probably  never  know 
what  did  happen.  However,  Macrocystis  has 
begun  to  return  to  the  Palos  Verdes  Penin- 
sula coincident  with  reduction  in  sludge 
and  DDT  discharge  from  the  White's  Point 
sewer  outfall  (Wilson  1982).  This 
suggests  that  sewage  pollution,  and 
particularly  increased  turbidity 
(Meistrell  and  Montagne  1983)  and  sludge 
accumulation  on  the  bottom  (Grigg  and 
Kiwala  1970),  had  important  direct  effects 
on  the  decline  of  giant  kelp  around 
southern  California  sewer  outfalls. 

Long-term  changes  in  central 
California  may  be  associated  with  changes 
in  the  abundance  and  distribution  of  sea 
otter  populations.  Van  Blaricom  (in 
press)  has  compared  canopy  distribution 
data  from  the  early  1900' s  (when  sea 
otters  were  essentially  absent)  with 
recent  surveys  (sea  otters  present).  He 
suggests  that  the  Macrocystis  canopy  area 
has  recently  increased  and  Nereocystis 
luetkeana  has  decreased  as  an  indirect 
result  of  sea  urchin  removal  by  sea 

The  production,  dispersal,  and 
recruitment  of  larvae  can  be  periodic 
phenomena.  Little  is  known  of  the 
relationship  of  production  and  dispersal 
to  recruitment  because  little  is  known 
about  larval  mortality,  particularly  for 
planktonic  larvae.  Large-scale  temporal 
patterns  of  some  invertebrate  (Dayton  and 
Tegner  1984a)  and  fish  distributions 
(Miller  and  Geibel  1973)  in  kelp  forests 
have  been  correlated  with  recruitment. 
Small  scale  patterns  in  sea  urchin  (North 
1983a),  Tegula  spp.  (Watanabe  1984a),  and 
spider  crab  (Hines  1982)  recruitment  have 
been  shown  or  suggested  as  important  to 
the  population  dynamics  of  these  species. 


On  a  shorter  time  scale  (1-5  years), 
changes  have  been  associated  with  year- 
to-year  variations  in  storm-swell 
intensity.  Ebeling  et  al.  (MS.)  has  made 
long-term  observations  of  a  kelp  forest  on 
an  isolated  reef  near  Santa  Barbara. 
Large  waves  in  1980-81  removed  most  of  the 
Macrocystis  from  the  reef.  Sea  urchins 
then  came  out  of  cracks  and  crevices  and 
actively  grazed  over  the  substratum.  This 
grazing  not  only  removed  most  of  the 
remaining  non-encrusting  algae,  but  also 
prevented  the  re-establishment  of  these 
plants.  The  more  severe  storms  of  1982-83 
reduced  the  abundance  of  these  exposed  sea 
urchins,  and  macroalgae,  including 
Macrocystis,  have  subsequently  recolonized 
the  area.  Ebeling  et  al.  (MS.)  found  that 
these  changes  also  affect  fishes,  particu- 
larly surfperch,  as  the  juveniles  use 
Pterygophora  cal ifornica  as  shelter  from 
predators,  and  the  adults  forage  for 
invertebrate  food  among  the  algae  that 
cover  the  bottom.  Abnormally  stormy  years 
can  also  have  dramatic  long-term  effects 
in  central  California,  altering  understory 
abundance  both  by  direct  removal,  and  via 
increased  light  from  surface  canopy 
removal  (Foster  1982a). 

There  have  been  historical  changes  in 
the  relative  abundance  and  distribution  of 
M.  pyrifera  and  Nereocystis  luetkeana  in 
central  California,  with  particular  sites 
changing  completely  or  partially  from 
giant  to  bull  kelp  and  vice  versa  (Yellin 
et  al.  1977,  Van  Blaricom  in  press). 
Numerous  causes  are  possible.  Storms 
appear  to  affect  surface  canopy  type,  with 
Nereocystis  replacing  Macrocystis  after 
the  latter  has  been  removed  by  severe 
water  motion  (Foster  1982a,  Van  Blaricom 
in  press).  In  addition,  variations  in  sea 
urchin  grazing  may  affect  species 
composition  (Van  Blaricom  in  press)  and 
kelp  forest  size  (Pearse  and  Hines  1979). 
Storms  can  also  indirectly  affect  entire 
forests,  as  storm-induced  sand  movement 
can  change  kelp  forests  into  soft-bottom 
communities  (North  1971b,  Grant  et  al. 
1982,  LOSL  1983). 

3.5.2  Short-Term  (<  1  year) 

The  relative  lack  of  large  seasonal 
changes  in  the  local  ocean  climate, 
particularly  storms,  appears  to  result  in 
reduced   seasonal   variability   in   kelp 

forest  communities  in  southern  California 
(Rosenthal  et  al.  1974,  SCE  1978).  These 
and  other  studies  (North  1971b,  Dean  pers. 
comrn. )  suggest  that  many  southern 
California  kelp  canopies  go  through  a 
three-  to  five-year  cycle  of  abundance  and 
decline,  perhaps  associated  with  holdfast 
deterioration  in  older  plants.  However, 
even  without  unusually  high  water  motion, 
mortality  of  adult  plants  is  about  40%  per 
year  in  the  kelp  forest  at  San  Onofre 
(Dean  pers.  comm. ) . 

In  central  California,  the  larger  and 
more  frequent  winter  swells  produce  a 
regular  seasonal  canopy  cycle  with  a 
maximum  canopy  size  in  summer,  and  a 
minimum  in  winter  (Miller  and  Geibel  1973, 
Gerard  1976,  Foster  1982a,  Reed  and  Foster 
1984,  Kimura  and  Foster  in  press).  These 
storms  can  also  influence  understory  algal 
abundance  (Foster  1982a).  Productivity, 
growth  rate,  and  recruitment  of  understory 
algae  also  change  seasonally  in  response 
to  climatic  conditions  and  cover  of 
surface  canopies  (Johansen  and  Austin 
1970,  Breda  1982,  Heine  1983,  Reed  and 
Foster  1984,  Kimura  and  Foster  in  press). 
Seasonal  changes  in  sand  cover  can  also  be 
important  (Breda  1982).  In  addition, 
juvenile  rockfish  commonly  recruit  into 
central  California  kelp  forests  during  the 
strong  upwelling  period  in  late 
spring-early  summer  (Miller  and  Geibel 
1973).  The  effects  of  seasonal  climatic 
changes  appear  to  increase  with  latitude, 
as  shown  in  the  distinct  summer-winter 
differences  in  Nereocystis  luetkeana 
forests  in  Washington  (Neushul  1967). 

3.5.3  Succession 

The  causes  of  both  long-  and 
short-term  changes  in  community 
composition,  such  as  spatial  patterns,  are 
a  complex  of  interacting  factors  of  which 
only  the  extremes  of  storms  and  grazing 
have  been  clearly  documented  in  particular 
forests.  These  disturbances  initiate 
successional  changes  that  remain  largely 
unexplored.  Foster  (1975a)  found  that 
successional  events  on  small  concrete 
blocks  placed  within  a  kelp  forest  were 
largely  determined  by  the  availability  of 
larvae  or  spores  in  the  water,  and 
differences  in  growth  rates  and 
competitive  abilities  among  colonizing 
species.   Aside  from  a  possible  initial 


enhancement  of  colonization  by  microalgal 
or  bacterial  films,  there  was  no  evidence 
for  facilitative  interactions  (sensu 
Connel 1  and  Slatyer  1977).  Macrocystis 
can  be  among  the  first  organisms  to  settle 
and  grow  if  spores,  space,  and  light  are 
adequate.  Similar  patterns  were  noted  by 
Fager  (1971)  on  isolated  structures  placed 
some  distance  from  a  kelp  forest,  while 
Kennelly  (1983)  has  shown  on  a  microscopic 
scale  that  most  species  associated  with  an 
Ecklonia  radiata  bed  in  Australia  have  the 
potential  of  quickly  recruiting  on 
artificial  substrata. 

The  above  examples  mimic  extreme 
disturbances  where  small  patches  of 
natural  substratum  are  completely  cleared. 
All  organisms  are  not  generally  removed 
during  normal  disturbances  in  kelp 
forests,  and  the  processes  involved  in 
succession  after  more  natural  disturbances 
remain  generally  uninvestigated  (see 
review  in  Foster  and  Sousa  in  press). 
Reed  and  Foster  (1984)  demonstrated  that, 
with  less  extreme  disturbance,  changes  in 
overstory  canopies  are  particularly 
important  to  subsequent  successional 
events.  Van  Blaricom  (in  press)  suggested 
that  in  central  California  Nereocystis 
luetkeana  first  colonizes  areas  where  sea 
otters  remove  sea  urchins  because  this 
annual  kelp  is  more  common  than 
Macrocystis  (i.e.,  more  spores  available 
for  colonization).  Macrocystis  then 
gradually  invades  these  areas,  and  in  the 
absence  of  storms  which  seem  to  have  a 
greater  impact  on  Macrocystis,  the 
perennial  giant  kelp  eventually  replaces 
bull  kelp,  as  the  canopy  of  the  former 
reduces  light  and  thereby  restricts 
recruitment  of  the  latter.  This  sequence 
may  be  altered  if  perennial  understory 
kelps  (Laminaria,  Pterygophora)  invade 
after  the  initial  disturbance  (storms, 
grazer  removal),  and  inhibit  further 
recruitment  (Van  Blaricom  in  press).  An 
increase  in  understory  foliose  red  algae 
could  also  inhibit  recruitment  of  all 
kelps  (Kimura  pers.  comm.). 

Various  other  interactions  may  also 
alter  succession.  Predators  may  directly 
alter  sessile  invertebrate  abundance 
(Foster  1975b,  Neushul  et  al.  1976)  and 
species  composition  (Day  and  Osman  1981), 
and  these  changes  may  indirectly  affect 
algal  succession  by  reducing  competition 

for  space  (Foster  1975b).  Grazing 
(probably  by  fish)  may  alter  algal  species 
composition  (Foster  1975b),  and  small 
algal  turf  species  may  facilitate  the 
survivorship  of  young  kelp  sporophytes  by 
providing  a  refuge  from  fish  grazing 
(Harris  et  al .  1984).  Small  herbivores 
may  alter  early  successional  patterns  in 
Ecklonia  radiata  beds  (Kennelly  1983, 
pers.  commTT  After  incomplete  removal  of 
sessile  organisms,  remaining  encrusting 
corallines  can  inhibit  recruitment  of 
numerous  sessile  invertebrates  (Breitburg 
1984),  and  encrusting  and  articulated 
corallines  may  inhibit  Macrocystis 
recruitment  (Wells  1983). 

Additional  effects  associated  with 
the  magnitude  and  extent  of  disturbance, 
micrograzers  and  predators,  sedimentation, 
etc.,  as  well  as  competition  for  light, 
dispersal,  and  basic  life  history 
characteristics  of  the  organisms  involved 
are  no  doubt  also  important  to  kelp  forest 
succession  (Foster  and  Sousa  in  press), 
but  remain  to  be  investigated  in  detail. 


3.6.1  Introduction 

Not  surprisingly,  giant  kelp 
communities  are  highly  productive; 
nutrients  are  generally  high  in  nearshore 
waters,  and  Macrocystis  can  form  a  dense, 
light-absorbing  canopy  at  the  water's 
surface.  The  production  of  Macrocystis, 
understory  kelps,  and  bottom-cover  algae, 
together  with  energy  imported  from  the 
plankton,  support  consumers  in  giant  kelp 
forests  as  well  as  in  nearby  communities 
receiving  drift  from  forests.  These 
processes,  as  well  as  food  webs  within  the 
Macrocystis  community,  are  reviewed  in 
detail  in  this  section. 

3.6.2  Biomass  (Standing  Stocks) 

Coon  (1982)  recently  compiled  the 
available  information  on  biomass  and 
productivity  of  eastern  north  Pacific 
Macrocystis.  Table  4  summarizes  these 
values  for  Macrocystis,  and  includes 
additional  estimates  for  understory  algae, 
sessile  invertebrates,  and  fishes.  Other 
than  the  few  quadrats  sampled  by  Aleem 


Table  4.   Kelp  forest  biomass/m2  of  bottom  (includes  water  column  from 
surface  to  bottom). 

Location                 Wet  kg/m2  Reference 

Macrocystis  pyrifera9 

La  Jolla,  California            6   -10  Aleem  1973 

Southern  California  and  Baja 

California,  Mexico              3   -22  North  1971b 

Paradise  Cove,  California        4.4  -  5.8  McFarland  and  Prescott  1959 

Goleta,  California             7   -  9  Coon  1982 

Pacific  Grove,  California        5.9  Towle  and  Pearse  1973 

Pacific  Grove,  California        0.7  -  6.3  Gerard  1976 

British  Columbiab              4.2  -  4.7  Field  and  Clark  1978 

Understory  Algae  (Other  Than  Macrocystis)  Within  Macrocystis  Forests 

La  Jolla,  California            4.8  Aleem  1973 

Bird  Rock,  California           0.47  North  1971b 

Paradise  Cove,  California        0.02-  0.5  McFarland  and  Prescott  1959 

Monterey,  California0           0.03-  0.7  Breda  1982 

Monterey,  California            2.0  Pearse  and  Hines  1976 

Monterey,  California            2.4  -  5.2  Gerard  and  Garrison  1971 

Santa  Cruz,  California0          0.07-  0.9  Breda  1982 

Santa  Cruz,  California          0.02-  0.04  Pearse  and  Hines  1979 

Benthic  Invertebrates 

Baja  California,  Mexico          0.6  Woollacott  and  North  1971 

La  Jolla,  California            0.11-  0.41e  Aleem  1973 

Monterey,  California           0.025-  0.37  Gerard  and  Garrison  1971 


Southern  California  and  Mexico    0.01-  0.046  Quast  1971b 

Pacific  Grove,  California         0.07-  0.11  Miller  and  Geibel  1973 

aModified  from  Coon  1982. 

Mixed  Macrocystis  integrifol ia  and  Nereocystis  luetkeana. 

Data  from  Breda  (1982)  for  red  algae  only,  and  converted  from  dry  weight 
values  (dry  =  0.12  wet) . 

Estimates  do  not  include  large,  mobile  invertebrates,  those  on  plants,  or 
those  living  in  kelp  holdfasts. 

Includes  mobile  invertebrates  on  the  bottom. 


(1973),  we  could  find  no  published  data  on 
the  biomass  of  mobile  invertebrates,  even 
though  these  animals  can  be  quite  abundant 
and  trophically  important  (see  below).  As 
Table  4  shows,  Macrocystis  biomass  can 
vary  by  more  than  an  order  of  magnitude. 
This  variation  is  probably  the  result  of 
differences  in  sampling  methods  and  sample 
size  (few  samples  in  a  patchy 
environment),  differences  in  sampling 
times,  and  real  differences  within  and 
among  kelp  forests.  Gerard's  (1976)  data 
are  most  representative  of  a  single  site 
as  she  sampled  over  2.5  years  in  the  same 
area,  and  found  that  giant  kelp  biomass 
varied  from  0.7  to  6.3  wet  kg/m2  (mean  = 
3.5).  This  large  within-forest  variation 
for  Macrocystis  (and,  when  determined, 
other  groups  of  organisms  as  well;  see 
below)  clearly  indicates  that  one  sampling 
cannot  characterize  biomass  in  these 
spatially  and  temporally  variable 

The  values  for  Macrocystis  can  be 
compared  with  other  temperate  nearshore 
kelp  communities.  Kain's  (1979)  review  of 
Laminaria  spp.  suggests  the  "typical" 
biomass  of  this  genus  in  Laminaria  beds  is 
-v.  10  wet  kg/m2  (range  2.5-20).  Similar 
values  have  been  found  for  mixed 
Ecklonia-Laminaria  beds  in  South  Africa 
(Vel imirov  et  al.  1977;  see  review  in  Mann 

The  biomass  of  understory  vegetation 
also  varies  considerably  (Table  4).  For 
these  plants,  the  data  of  Breda  (1982) 
from  two  sites  in  central  California  are 
most  indicative  of  possible  seasonal 
variation  at  a  single  site:  an  order  of 
magnitude  in  one  year.  However,  these 
relatively  long-term  studies  by  Gerard 
(1976)  and  Breda  (1982)  were  done  in  cen- 
tral California  where,  as  discussed  in 
Section  3.5,  storm-related  variability 
appears  to  be  greater  than  in  southern 
California.  As  for  percentage  cover  (see 
Section  2.4),  understory  algal  biomass  is 
usually  lower  beneath  than  away  from  a 
giant  kelp  canopy  (North  1971b,  Aleem 
1973)  and,  in  the  absence  of  a  canopy, 
generally  decreases  with  depth  (Aleem 

Few  estimates  of  the  biomass  of 
sessile  benthic  invertebrates  or  fish  have 
been  made  (Table  4),  and  none  over  long 

periods  of  time.  Miller  and  Geibel  (1973) 
suggested  that  their  relatively  high  fish 
estimates  for  central  California  versus 
those  for  southern  California  (Table  4) 
could  be  due  to  differences  in  sampling 

3.6.3.  Primary  Productivity 

Macrocystis  pyrifera  is  a  large  plant 
with  a  complex  morphology  and  its  primary 
productivity  is  difficult  to  measure.  A 
variety  of  techniques,  including  field 
harvests  (Clendenning  1971b),  growth 
measurements  (Gerard  1976),  changes  in 
oxygen  content  of  forest  water  (McFarland 
and  Prescott  1959,  Jackson  1977),  field 
measurements  of  radioactive  carbon  uptake 
(Towle  and  Pearse  1973),  and  extrapola- 
tions from  laboratory  measurements 
(Wheeler  1978)  have  been  used  to  estimate 
the  productivities  in  Table  5.  No  doubt 
some  of  the  variability  in  Table  5  is  the 
result  of  technique  (suggested  by  the 
greater  similarity  of  estimates  using  the 
same  technique). 

Again,  because  of  the  long-term 
nature  of  the  study,  Gerard's  (1976)  data 
are  perhaps  most  representative  of  true 
productivity,  even  though  she  did  not 
account  for  grazing,  detrital,  or 
dissolved  organic  matter  losses  (see 
Section  3.6.4  below).  Based  on  frond 
addition  and  growth  measurements,  Gerard 
(1976)  found  monthly  productivity  to  vary 
between  0.4  and  3.0  wet  kg/m2,  with  an 
average  of  23  wet  kg/m2/yr.  Using  the 
conversion  factors  from  Coon  (1982)  given 
in  Table  5,  this  is  equivalent  to  2.8  kg 
dry  wt.,  or  530  g  C(carbon)/m2/yr. 
However,  there  is  some  disagreement 
between  conversion  factors  for  wet  weight- 
carbon  as  Towle  and  Pearse  (1973)  use  a 
factor  of  0.036.  With  this  higher  value, 
Gerard's  (1976)  productivity  is  828  g 
C/m2/yr.  In  either  case,  these  values  are 
within  the  range  of  the  more  productive 
marine  macrophyte  communities  (Mann  1973, 
1982).  Macrocystis  biomass  can  also  turn 
over  rapidly  ("productivity  [23  wet 
kg/m2/yr]/biomass  [3.5  wet  kg/m2] 
turnover  of  6.6  times/yr). 

Mann  (1982,  pp.  59  and  60)  suggested 
that  large  kelps  like  Macrocystis  should 
have  a  low  P/B  (productivity/biomass) 


Table  5.   Macrocystis  pyrifera  net  primary  productivity   (see  text  for 
discussion  of  technique). 


Wet  kg/m2/year 


Field  Growth 
Santa  Barbara,  California 
Monterey,  California 
Palos  Verdes,  California 
Southern  California 

Physiological  Estimates 
Paradise  Cove,  California 
Santa  Barbara,  California 
San  Diego,  California 
Monterey,  California 

Harvest  Estimates 
Southern  California 
Santa  Barbara,  California 


Coon  1981 


Gerard  1976 


Kirkwood  1977 


Clendenning  1971b 


McFarland  and  Prescott  1959 


Wheeler  1978 


Jackson  1977 


Towle  and  Pearse  1973 


Clendenning  1971b 


Coon  unpubl .  data 

Based  on  Coon  1982;  net  primary  productivity 

For  rough  conversions  to  other  units,  dry  wt. 
gC(carbon)  =  (0.023)  g  wet  wt.  (Coon  1982). 

'Based  on  biomass  of  7  wet  kg/m2 . 

gross  primary  production  - 
=  0.12  wet  wt.  (Coon  1982), 

ratio  because,  relative  to  plants  like 
Laminaria,  Macrocystis  diverts  large 
amounts  of  energy  to  respiration  and 
structural  repair.  We  are  unaware  of  any 
data  that  show  this  diversion  is  greater 
in  plants  like  Macrocystis,  and  Gerard's 
(1976)  data  discussed  above  show  that  this 
P/B  ratio  can  be  similar  to  ratios  given 
for  Laminaria  (Mann  1982).  Thus,  Mann's 
(1982)  suggestion  that  the  net  production 
of  kelp  beds  is  greater  than  kelp  forests 
is  probably  incorrect. 

Heine  (1983)  measured  the  hi  situ 
productivity  of  two  common  understory  red 
algae,  Botryocladia  pseudodichotoma  and 
Rhodymenia  californica,  in  the  Point 
Cabrillo  kelp  forest  in  central 
California.  However,  rates  were  expressed 

per  gram  dry  weight  of  tissue  and  measured 
over  small  time  intervals  so  yearly 
production  per  unit  area  of  bottom  cannot 
be  calculated.  We  thus  have  no  estimates 
of  yearly  understory  algal  production  for 
giant  kelp  forests. 

The  summary  of  productivity  suggests 
that  if  total  net  macroalgal  primary 
productivity  (Macrocystis  plus  all 
understory  algae]  Ts  ever  measured  in  a 
densely  vegetated  giant  kelp  forest,  it 
may  be  the  highest  of  any  marine 
community.  This  might  be  expected, 
because  most  of  the  biomass  of  giant  kelp 
is  near  the  surface  where  light  is 
highest,  and  carbon  fixed  at  the  surface 
is  translocated  to  parts  of  the  plants  at 
lower  light  intensities  below  (see  Chapter 


4,  Section  Nutrients  needed  for 
growth  are  also  frequently  high  in  the 
nearshore  waters  where  these  plants  occur 
(see  Chapter  2,  Section  2.5).  Finally, 
the  community  is  always  submerged  in 
waters  of  near-constant  salinity.  Thus, 
unlike  other  productive  communities  such 
as  estuarine  sea  grass  beds  or  mangrove 
forests,  plants  in  the  kelp  forest  have 
relatively  little  non-photosynthetic 
support  tissue  and  do  not  use  much  of  the 
energy  produced  for  osmoregulation  to 
adapt  to  periodic  emergence-submergence. 

The  final  source  of  primary 
production  in  giant  kelp  forests  is  phyto- 
plankton.  To  our  knowledge,  phytoplankton 
production  within  a  forest  has  never  been 
estimated.  Evidence  from  other  studies, 
however,  suggests  it  is  small  relative  to 
the  seaweeds.  Piatt  (1971)  estimated 
phytoplankton  production  at  about  200  g 
C/m2/yr  in  a  bay  in  Nova  Scotia,  where  the 
Laminaria  beds  averaged  about  1500  g 
C/m2/yr  (Mann  1973).  Clendenning' s 
(1971b)  estimates  for  phytoplankton 
production  in  southern  California  coastal 
waters  are  similar.  Shading  no  doubt 
would  reduce  these  values  under  a  surface 
canopy.  Phytoplankton  production,  at 
least  around  areas  of  kelp,  is  low 
compared  to  the  macroalgae,  but  is  in  the 
range  of  values  given  by  Ryther  (1969)  as 
typical  of  phytoplankton  in  nutrient-rich 
upwelling  areas  unshaded  by  a  surface 
seaweed  canopy. 

3.6.4  Energy  Flow  -  Food  Webs 

The  net  primary  production  of 
seaweeds  in  a  kelp  forest  is  available  to 
consumers  in  three  forms:  (1)  living 
tissue  on  attached  plants,  (2)  drift  in 
the  form  of  whole  plants  or  detached 
pieces,  and  (3)  dissolved  organic  matter 
exuded  by  attached  and  drifting  plants. 
Detritus  is  very  small  pieces  of  drift 
algae,  and  particulate  organic  matter 
(POM)  is  even  smaller  pieces.  Both  these 
subcategories  may  be  derived  from  attached 
plants  or  from  the  breakdown  of  drift. 
The  fate  of  these  forms,  plus  within- 
forest  phytoplankton  production  and 
imported  sources  of  energy  (plankton  and 
drift  seaweed  from  other  areas),  is 
illustrated  in  the  generalized  kelp  forest 
food  web  of  Figure  11. 

Gerard  (1976)  determined  the  general 
disposition  of  Macrocystis  productivity 
(attached  plants  and  drift)  in  the  Point 
Cabrillo  kelp  forest.  She  estimated  that 
of  the  yearly  production  (excluding 
grazing,  detritus,  and  dissolved  organic 
matter  losses  from  attached  plants),  70% 
entered  the  consumer  assemblage  as  drift. 
Of  this,  an  estimated  40%  was  utilized 
within  the  forest,  and  50%  was  transported 
out.  This  latter  figure  is  of  interest  as 
this  exported  production  may  end  up  on 
nearby  shores  where  it  is  an  important 
source  of  energy  for  beach  invertebrates 
and,  ultimately,  for  shore  birds  (Yaninek 
1980,  North  1971b;  see  Chapter  4,  Section 
4.6).  Detached  Macrocystis  and  other 
macroalgae  may  also  drift  offshore  along 
the  bottom  where  they  presumably  serve  as 
food  (North  1971b)  and  habitat  (Cailliet 
and  Lea  1977)  for  deep-water  organisms 
living  where  light  is  insufficient  for  in 
situ  photoautotrophic  productivity. 
Plants  may  drift  offshore  on  the  surface 
as  kelp  rafts  that  provide  habitat  for 
juvenile  and  some  adult  fishes  (Mitchell 
and  Hunter  1970). 

Gerard  (1976)  also  estimated  that 
only  ^  3%-6%  of  the  total  Macrocystis 
production  was  consumed  directly  by 
animals  grazing  on  attached  plants. 
Direct  detrital  loss  was  not  measured, 
although  it  may  be  an  important  form  of 
primary  production  entering  the  community, 
particularly  from  senescent  fronds.  Esti- 
mates of  dissolved  organic  matter  (DOM) 
produced  by  large  seaweeds  are  highly 
variable,  and  may  partly  be  an  artifact  of 
handling  and  laboratory  technique 
(Fankboner  and  de  Burgh  1977). 

Little  is  known  about  the  precise 
fate  of  drift  algae  in  giant  kelp  forests, 
other  than  it  can  be  eaten  without 
decomposition  by  large  herbivores  like  sea 
urchins  and  abalone  (see  Section  4.4.3). 
The  experiments  by  Bedford  and  Moore 
(1984)  in  Laminaria  saccharina  beds  in 
Scotland  show  that  much  of  the  drift  is 
not  decomposed  by  microbes  but,  instead, 
eaten  by  small  detritivores  (echinoderms, 
polychaetes,  and  amphipods).  Decomposi- 
tion by  microbes  increased  when  these 
detritivores  (that  would  otherwise  crop 
rotting  tissue  or  repeatedly  remove 
healthy  tissue  preventing  microbial 
colonization)  were  excluded.   In  contrast 



1°  Producers 
+  Import  from 
Drift  and 

1°  Consumers 

2°  Consumers 

3°  Consumers 

Imported  drift 

; export; 

Benthic  algae 



Herbivorous  fish 
and  crabs 

Sea  stars 

Vertebrate  predators 

Sharks  and  rays 
Harbor  seals 


DOM = dissolved  organic  matter. 

Invertebrate  detritus 
Brittle  stars 
Sea  cucumbers 

Vertebrate  predators 


Kelp  bass 





Sharks  and  rays 

■  Parasites 

Al 1  above 



Imported  and  resident 


Invertebrate  filter- 
suspension  feeders 
Cora  1  s 


Vertebrate  predators 
Juv.  and  adult 

POM  = particulate  organic  matter. 

(as  above) 

Invertebrate  detritus 
and  filter-suspension 
(as  above) 

Figure  11.  A  generalized  food  web  for  a  kelp  forest, 
energy  flow. 

Arrows  indicate  the  direction  of 

to  vascular  plants,  Bedford  and  Moore 
(1984)  point  out  that  drift  seaweeds  have 
few  structural  polysaccharides,  lack  waxy 
coverings,  and  may  exude  fewer  protective 
chemicals,  making  them  more  directly 
palatable  to  detritivores.  This  suggests 
that  the  fate  of  subtidal  algal  drift 
(directly  to  detritivores)  may  be 
fundamentally  different  from  that  of 
vascular  plant  detritus  (through  microbes 
to  detritivores).  Furthermore,  this 
difference  may  be  ultimately  reflected  in 
the  high  abundances  of  fish  in  kelp 
forests;  many  of  these  fish  feed  on  small 
crustaceans   and   polychaetes   that   are 

probably   detritivores  and  4.5). 

(see   Sections 

Our  understanding  of  energy  flow 
through  the  remainder  of  the  giant  kelp 
forest  community  is  based  largely  on 
feeding  observations,  with  few  quantita- 
tive studies.  Rosenthal  et  al .  (1974) 
constructed  a  food  web  from  feeding 
observations  in  a  kelp  stand  near  Del  Mar 
which,  with  additions  from  observations 
made  in  other  areas,  is  summarized  in  the 
generalized  giant  kelp  forest  food  web  of 
Figure  11.  As  might  be  expected  from  the 
variety  of  ways  energy  can  enter  the 


consumer  assemblage  and  the  number  of 
different  species  in  the  assemblage, 
feeding  relationships  can  be  complex.  All 
of  the  pathways  shown  have  been  verified 
by  feeding  observations  or  gut  content 
studies,  and  in  addition,  Fankboner  (1976) 
and  Fankboner  and  Druehl  (1976)  have  shown 
that  at  least  two  invertebrates  can  use 
dissolved  organic  matter  produced  by 
Macrocystis  integrifolia. 

Biomass,  densities,  and  feeding 
observations  have  been  used  by  Pearse  and 
Hines  (1976)  to  construct  a 
semi-quantitative  food  web  for  the  Point 
Cabrillo  kelp  forest  that  shows  standing 
stocks  and  feeding  relationships  (Figure 

In  our  view,  productivity  and  energy 
flow  in  communities  are  a  consequence,  not 
a  cause,  of  population  and  community 
structure.  As  a  subdiscipl ine  of  ecology 
they  may  be  of  interest  in  their  own 
right,  but  they  have  contributed  little  to 
our  understanding  of  community  structure 
and  dynamics.  Moreover,  food  webs 
constructed  from  energy  flow  studies  can 
be  misleading  as  they  may  be  interpreted 
as  "control  webs";  because  A  eats  B,  A 
controls  the  population's  size  and/or 
distribution  of  B.  Such  a  misinterpre- 
tation of  food  webs  has,  no  doubt, 
contributed  to  the  popular  notion 
(probably  misconception  --  see  Ehrlich  and 
Birch  1967,  Connell  and  Sousa  1983,  Wiens 
1984)   that   "nature   is   in   balance." 

I  vermetids    snails    abalone    bat  stars    sea  urchins    crabs 

50  000        200.  4.000  5.000 


detritus     grazing 

Cystoseira  \    giant  kelp    / 

2.000  500 

(veg:  500  kg)  (3,000  kg) 

(net  production:  24,000  kg/yr) 

red  algae 
(1.500  kg) 

Figure  12.  A  food  web  for  the  Point  Cab- 
rillo kelp  forest  near  Monterey.  Numbers 
give  approximate  number  of  organisms/ 
1000  m2.  Numbers  in  parentheses  give 
approximate  wet  weight/1000  m2  (from 
Pearse  and  Hines  1976). 

Populations  may  be  regulated  by  predators 
or  grazers,  but  they  can  also  be  regulated 
by  a  variety  of  other  processes.  Figure 
13  illustrates  some  of  the  "control" 
possibilities  discussed  in  detail 
elsewhere  in  this  profile  (see  especially 
Chapters  2  and  5),  many  of  which  are  not 
easily  measured  in  equivalent  energy  units 
(e.g.,  a  storm  removing  a  large  quantity 
of  kelp  or  killing  sea  urchins),  or  affect 
such  small  amounts  of  energy  that  they  are 
not  usually  considered  in  even  a  detailed 
energy  flow  analysis  (e.g.,  spore  or 
larval  removal  by  filter  feeders). 




Affects  Distribution, 
and  Abundance  of 






on  Spores 
and  Gametes 



on  Larvae  / 


Benthic  Algae  c 

|    Competition 
v~5   Space 


on  Larvae 




-  PCDD 

'      Food 



^   Food 

PCDD  =  Physical/Chemical  Environment,  Dispersal,  Disease 
1  =  Inhibition  of  feeding  by  presence  of  fronds 

Figure  13.  Generalized  control  web  of  factors  and  interactions  affecting  the  distribu- 
tion and  abundance  of  organisms  in  a  kelp  forest. 




The  number  of  living  creatures  of  all  Orders  whose  existence 
intimately  depends  on  the  kelp  is  wonderful.  Darwin  (1860). 


This  chapter  discusses  most  of  the 
common  species  of  algae,  invertebrates, 
fish,  birds,  and  mammals  that  frequent 
Macrocystis  forests  or  are  an  integral 
part  of  them  along  the  west  coast  of  North 
America.  Where  relevant,  we  also  include 
comparisons  with  other  regions  of  the 
world.  This  chapter  is  not  meant  to 
provide  comprehensive  species  checklists 
of  the  organisms  which  may  occur  in  kelp 
forests;  these  may  be  obtained  from  other 
sources  referred  to  in  the  appropriate 
sections  below.  Rather,  we  discuss  the 
natural  history  of  many  species  and 
they  may  function  in,  or  contribute 
the  structure  of  kelp  forests 
particular  localities.  We  divide 
ubiquitous  and  diverse  benthic  inverte- 
brates and  seaweeds  into  functional 
categories,  grouping  species  which  we 
subjectively  judge  to  have  similar  effects 
on  the  other  species  present.  These 
categories  are  then 
taxonomic  groups, 
decomposers  and  diseases 
separate  sections,  as  are 





separated  into 
Plankton  and 
are  treated  in 

fish,  birds,  and 


As  might  be  expected  given  the 
diversity  of  large  plants  and  animals  in 
giant  kelp  forests,  attention  has  focused 
on  these,  and  relatively  little  is  known 
about  the  small  plants  and  animals  that 

constitute  the  planktonic  assemblage  in 
the  water.  Clendenning  (1971a)  gave  a 
brief  list  of  phytoplankton  from  the  La 
Jolla  kelp  forest,  and  Miller  and  Geibel 
(1973)  discussed  the  seasonal  abundance  of 
various  plankton  groups  (especially 
zooplankton)  in  the  kelp  forest  at  Point 
Cabrillo  near  Monterey,  California. 
Additional  studies  have  examined 
zooplankton  in  relation  to  fish  feeding 
(Hobson  and  Chess  1976,  Bray  1981,  Bray  et 
al.  1981)  or  migratory  behavior  (Hobson 
and  Chess  1976,  Hammer  and  Zimmerman  1979, 
Hammer  1981).  There  are  no  complete 
identification  guides.  Cupp  (1943)  is 
still  the  best  available  guide  to  the 
diatoms,  and  the  text  by  Newell  and  Newell 
(1963)  is  useful  for  identifying  the  more 
common  phyto-  and  zooplankton.  Parsons  et 
al.  (1977)  reviewed  planktonic  organisms 
and  the  oceanographic  processes  that 
affect  them,  and  provide  an  excellent 

As  shown  in  Figure  11,  plankton  may 
be  produced  in  the  kelp  forest  or  imported 
(primarily  from  offshore).  With  the 
exception  of  some  mysids  (discussed 
below),  few  entirely  planktonic  organisms 
(holoplankton)  appear  to  be  residents  of 
kelp  forests;  most  are  probably  imported. 
The  kelp  forest  community  produces 
plankton  in  three  general  categories: 
meroplankton--the  spores,  larvae,  or 
detached  individuals  (e.g.,  benthic 
diatoms)  of  benthic  organisms;  demersal 
zooplankton  --  primarily  small  crustaceans 


that  migrate  between  the  benthos  and  the 
water  column  above;  and  mysids  that  may  be 
in  both  of  these  categories  as  well  as 
being  holoplanktonic. 

Even  less  is  known  about  bacteria  and 
fungi  that  decompose  organic  matter  within 
kelp  forests.  These  organisms  and  the 
materials  they  produce  and  degrade  are 
probably  important  sources  of  food  for  the 
largely  detritus-based  food  web,  but 
perhaps  less  important  than  direct 
consumption  of  drift  algae  by  detritivores 
(see  Section  3.6.4).  General  character- 
istics of  surface  bacteria  and 
decomposition  by  bacteria  and  fungi  are 
briefly  discussed  by  Scotten  (1971)  and 
ZoBell  (1971). 

General  composition  and  natural 
history  of  the  more  abundant  kelp  forest 
plankton  are  discussed  below. 

4.2.1  Phytoplankton 

Probably  all  species  of  phytoplankton 
found  in  nearshore  waters  could  be  found 
in  kelp  forests  at  some  time  and  there 
appear  to  be  no  species  endemic  to  kelp 
forests.  Clendenning  (1971a)  listed  58 
species  of  diatoms  and  dinoflagellates 
collected  from  the  La  Jolla  kelp  forest  in 
June  1958,  with  the  diatom 
Leptocyl indricus  spp.  and  the 
dinoflagel late  Diplopel topsis  minor  most 
abundant.  Miller  and  Geibel  (1973)  did 
not  identify  phytoplankton  to  the  species 
level  in  their  study  of  the  Point  Cabrillo 
kelp  forest,  but  they  stated  that  the 
diatom  genera  Coscinodiscus  and 
Rhizosolenia  were  most  commonly  observed. 

Various  species  of  benthic  diatoms 
are  also  found  in  the  plankton,  particu- 
larly after  storms  when  individuals  or 
"chains"  have  been  dislodged  by  water 
motion.  The  most  common  species  are 
Licmophora  abbreviata,  Meloseira 
monil iformis,  and  the  large,  angular 
Isthmia  nervosa  (Figure  14).  The  former 
is  particularly  common  on  giant  kelp 
blades.  When  attached,  these  and  other 
benthic  species  often  form  soft,  hair-like 
coverings  on  senescent  macroalgae, 
attached  understory  plants,  and  unoccupied 
hard  substrata  if  light  intensity  is  high. 
If  the  water  is  calm  and  light  is  high  for 
long  periods,  other  diatoms  may  form  thin 

Figure  14.   Common 
mysid  shrimp. 

benthic  diatoms  and  a 

brown  films  or  even  thick  mats  on  patches 
of  soft  substrata  within  a  kelp  forest. 
We  commonly  observe  late  spring  "blooms" 
of  benthic  diatoms  on  understory 
articulated  corallines  in  Carmel  Bay, 
California,  when  the  overstory  canopies  of 
Pterygophora  cal  ifornica  and  Macrocystis 
pyrifera  are  still  reduced  from  winter 
storms.  When  connected  in  long  chains  or 
in  a  common  mucilagenous  sheath,  these 
diatoms  may  be  confused  with  small, 
filamentous  brown  algae  whose  external 
form  can  be  similar. 

Planktonic  and  benthic  diatoms  are 
consumed  by  filter  feeders  and  grazers, 
but  little  is  known  about  consumption 
rates  or  consumer  feeding  preferences  in 
kelp  forests.  Trotter  and  Webster  (1984) 
have  shown  that  free-living  nematodes 
associated  with  Macrocystis  integrifol ia 
eat  bacteria  and  diatoms,  and  that 
particular  species  of  nematodes  may  prefer 
one  food  source  or  the  other,  and  may  also 
prefer  particular  species  of  diatoms. 

Dinoflagellates  may  become  extremely 
abundant  in  kelp  forests  during  red  tides 
(up  to  20  x  106  cells/liter;  Holmes  et  al. 
1967).  An  extensive  nearshore  bloom  of 
Ceratium  sp.  occurred  in  the  vicinity  of 
Monterey,   California    in   August   and 


September  1980  (Foster  and  Heine  1981). 
When  water  containing  this  bloom  moved 
into  the  kelp  forests,  visibility  was 
reduced  to  zero  on  the  bottom.  Whether  or 
not  they  produce  a  bloom,  some  dino- 
flagellate  species  are  toxic  to  man.  As 
dinoflagel lates  are  usually  most  abundant 
in  summer  and  early  autumn,  harvesting  of 
filter  feeding  shellfish  (particularly 
mussels)  that  may  concentrate 
dinoflagel lates  is  banned  during  this 

Phytoplankton  reduce  water  clarity 
and  therefore  contribute  to  the  reduction 
of  light  within  kelp  forests  (see  Chapter 
2).  Because  phytoplankton  growth  is  often 
stimulated  by  increased  nutrients,  these 
organisms  may  be  particularly  abundant 
around  sewer  outfalls  (Eppley  et  al .  1972, 
Kleppel  et  al.  1982),  and  along  with 
increased  turbidity  from  suspended  solids, 
can  affect  macroalgal  populations  by 
reducing  light.  Reduced  light  associated 
with  the  Los  Angeles  sewer  discharge  at 
White  Point  may  have  contributed  to  the 
loss  of  kelp  forests  at  Palos  Verdes 
(Wilson  1982). 

4.2.2.   Zooplankton 

Almost  all  nearshore  zooplankton 
species  can  also  be  found  in  kelp  forests 
at  various  times.  Holoplanktonic  species 
can  be  an  important  source  of  food  for 
some  kelp  forest  fishes  (particularly  the 
blacksmith;  Bray  1981;  see  Section  4.5 
below),  and  are  imported  as  energy  and 
nutrients  into  the  kelp  forest  from 
planktonic  communities  as  fish  feces  (Bray 
et  al .  1981).  Zooplankton  may 
occasionally  have  dramatic  effects  on  kelp 
forests.  Duggins  (1981a)  described  a 
reduction  in  sea  urchin  grazing  on 
macroalgae  in  Alaska  caused  by  an  increase 
in  benthic  diatoms  and  an  influx  of 
pelagic  salps.  The  sea  urchins 
temporarily  fed  on  the  diatoms  and  salps, 
grazing  on  macroalgae  decreased,  and 
macroalgal  abundance  increased. 

One  group  of  zooplankton,  the  mysids 
or  opossum  shrimp  (Figure  14)  are  usually 
associated  with  kelp  forests,  and  can  form 
extremely  dense,  migrating  swarms  on  the 
bottom  or  under  the  Macrocystis  surface 
canopy  (Clarke  1971).  Individuals  may  be 
up  to  2  cm  long,  and  swarms  may  be 

extensive  (meters  thick  and  wide)  and  so 
dense  as  to  obscure  the  bottom  completely. 
Mysids  apparently  feed  on  both  small 
plankton  and  macroalgal  detritus,  and  are 
fed  upon  by  many  kelp  forest  fishes 
(Clarke  1971),  and  even  gray  whales  (see 
Section  below). 

In  addition  to  the  above  zooplankton, 
there  is  an  assemblage  of  primarily  small 
crustaceans  that  migrate  at  night  from  the 
bottom  up  into  the  water  column  (Hobson 
and  Chess  1976,  Hammer  and  Zimmerman  1979, 
Hammer  1981).  These  demersal  zooplankton 
often  use  bottom  cover  algae  as  habitat 
during  the  day,  and  at  Catalina  Island  at 
least,  are  fed  upon  in  the  plankton  at 
night  by  a  variety  of  fishes  (Hobson  and 
Chess  1976). 


4.3.1  Introduction 

The  west  coast  of  North  America  is 
unique  in  the  number  of  subtidal  algal 
species  that  form  canopies  extending  to 
the  surface  of  the  sea,  and  perhaps  with 
the  exception  of  Australia,  in  the  number 
of  species  which  form  an  understory  canopy 
1-2  m  high.  Most  of  these  are 
Laminariales  of  the  families  Alariaceae, 
Laminariaceae,  and  Lessoniaceae  (Druehl 
1970).  The  distribution  of  surface  canopy 
species  is  discussed  in  Chapter  3,  along 
with  depth-distribution  patterns. 

Within  any  kelp  forest,  the  vertical 
stratification  of  canopy  levels  in  the 
water  column  is  an  obvious  feature  to  any 
observer.  The  density  of  the  vegetation 
layers  may  have  several  effects  in  a  kelp 
forest.  The  biomass  and  vertical 
structuring  they  form  provide  a  nursery 
and  protective  cover  for  many  species  of 
fish  (Quast  1971a).  These  layers  may 
sequentially  reduce  the  light  that  reaches 
primary  substratum  to  <  1%  of  surface,  a 
reduction  that  may  affect  the  recruitment 
and  growth  of  algal  species  (see  Chapter 
2).  Water  motion  may  also  be  altered 
within  dense  stands  by  the  kelp  themselves 
(see  Section  2.6).  The  result  of  inter- 
actions of  environmental  and  biotic 
factors  is,  therefore,  quite  complex. 
While  the  presence  of  recruits  of  a 
species  and  subsequent  growth  rates  and 
survival   may  be  directly   related  to 


features  of  the  environment  (see  Chapters 

2  and  5),  plants  may  also  change  these 

features   as   they   grow  and   spread 

vertically  through  the  water  column. 

Following  Foster  (1975a),  we  have 
divided  the  kelp  forest  vegetation 
functionally  into  four  layers  above  the 
primary  substratum  (Figures  3  and  6): 
encrusting  species,  filamentous  and 
foliose  species,  understory  Laminariales 
and  Fucales,  and  the  species  forming 
surface  canopies.  Each  of  these  levels 
will  have  an  effect  on  the  recruitment, 
growth  and  survival  of  species  below,  and 
because  all  start  life  on  the  bottom,  on 
themselves.  Complete  descriptions  of 
California  seaweeds,  including  geography 
and  depth  distributions,  can  be  found  in 
the  taxonomic  work  by  Abbott  and 
Hollenberg  (1976),  and  the  biology  and 
natural  history  of  the  most  abundant 
species  in  Dawson  and  Foster  (1982).  The 
more  common  species  are  discussed  below. 

4.3.2  Species  That  Form  Surface  Canopies: 
Kelp  Forests  Macrocystis.  The  morphology 
and  typical  Laminariales  life  history  of 
Macrocystis  is  outlined  in  Chapter  1  (see 
Figure  1).  To  grow  into  mature 
sporophytes,  microscopic  spores  must 
alight  on  suitable  substratum,  develop 
into  gametophytes ,  become  fertilized,  then 
grow  from  a  microscopic  sporophyte  through 
the  water  column  to  the  surface  of  the 
sea.  The  hazards  encountered  during  the 
course  of  this  development  are  numerous 
(see  Chapter  5),  and  it  is  not  surprising 
that  few,  if  any,  of  the  billions  of 
spores  produced  by  a  single  mature  plant 
ever  make  it  through  all  of  these  stages. 
Sedimentation,  the  pre-emption  of  space  by 
other  species,  the  lack  of  light  and 
shading  effects  of  other  species,  nutrient 
limitation,  and  the  effects  of  various 
small  and  large  grazers  are  some  of  the 
factors  which  affect  the  growth  and 
survival  of  plants. 

Macrocystis  and  the  other  large 
kelps,  by  virtue  of  their  high  growth 
rates  and  sizes,  are  able  to  modify  their 
circumstances  to  a  much  greater  degree 
than  smaller  seaweeds.  It  is  true  to  some 
extent  for  any  species  that  the 
devastating  effects  of  many  factors  may  be 

outgrown.  For  example,  a  relatively  small 
amount  of  sediment  on  the  substratum  may 
prevent  the  attachment  of  algal  spores, 
and  may  also  remove  over  98"  of  the 
incident  irradiance  from  reaching  the 
substratum  (Devinny  and  Volse  1978,  Norton 
1978).  Once  a  plant  survives  to  a 
juvenile  stage  of  even  a  few  millimeters 
height,  however,  the  effect  of  fine 
sediment  may  be  greatly  reduced.  The 
larger  members  of  the  Laminariales  and 
Fucales  can  take  advantage  of  the 
progressively  increasing  light  levels  as 
they  grow  through  the  water  column.  This 
involves  an  increase  in  the  spectra  of 
light  available  as  well  as  the  intensity 
(Wheeler  1980a,  Luning  1981).  Blades  that 
lie  near  the  surface  of  the  sea  may  take 
better  advantage  of  sunlight,  minimizing 
the  absorptive  effects  from  sea  water  or 
other  species  of  algae.  In  the  case  of 
Macrocystis,  this  is  borne  out  by  the  fact 
that  most  of  the  biomass  is  concentrated 
at  the  surface  in  the  upper  20%-30%  of  the 
plant  where  most  of  the  photosynthesis 
occurs  (Lobban  1978;  Plates  1A,  IB). 
North  (1972b)  found  that  this  concentra- 
tion of  biomass  at  the  surface  occurs 
regardless  of  water  depth.  Translocation 
through  phloem-like  sieve  tubes  moves 
fixed  carbon  (primarily  mannitol),  and 
proteins  down  surface  fronds  to  the 
holdfast  and  short,  understory  fronds 
(Parker  1971,  Lobban  1978). 

The  early  growth  of  Macrocystis 
pyrifera  in  southern  California  has  been 
described  by  Neushul  and  Haxo  (1963), 
North  (1971a),  and  Dean  et  al .  (1983). 
Giant  kelp  fronds  may  elongate  at  a  rate 
of  over  30  cm/day,  making  it  one  of  the 
fastest-growing  plants  known  (North 
1971c).  Neushul  (1963)  estimated  that  it 
took  14  months  from  sporulation  to 
maturity  for  plants  in  southern 
California.  Plants  may  live  up  to  8  years 
(North  1971a,  Rosenthal  et  al .  1974). 
Rosenthal  et  al.  (1974)  recorded  the 
survivorship  of  a  cohort  of  Macrocystis 
pyrifera  plants  in  the  Del  Mar  kelp 
forest,  over  a  period  of  3.5  years  (Figure 
15).  They  found  that  there  was  a  high 
mortality  rate  in  the  first  few  months 
after  recruitment,  but  that  this  decreased 
when  plants  were  a  year  old.  Five  out  of 
the  original  cohort  of  156  plants  survived 
after  one  year.  Dayton  et  al .  (1984) 
constructed  a  life  table  for  a  Macrocystis 








10  - 








(1970)  (1971) 



Figure  15.  A  survivorship  curve  for 
individually-tagged  Macrocystis  pyrifera 
plants  that  recruited  to  a  kelp  forest  off 
Del  Mar,  California  in  September  1969. 
The  original  cohort  was  387  plants  (re- 
drawn from  Rosenthal  et  al.  1974). 

population  at  a  depth  of  15  m  in  the  Point 
Loma  kelp  forest.  They  found  that  only 
19%  of  plants  survived  the  first  three 
months  after  recruitment,  and  2%  after 
nine  months.  Some  plants  survived  to  an 
age  of  7  years.  The  life  span  of  fronds, 
however,  is  only  about  6  months  (North 

Kain  (1982)  compared  the  short-term 
growth  rates  of  fronds  of  Macrocystis 
pyrifera  from  three  sites  in  southern  New 
Zealand  with  those  at  a  site  in  southern 
California.  The  relative  growth  rates  of 
stipes  and  laminae  from  the  different 
populations  were  similar.  By  a  series  of 
morphometric  measurements,  however,  Kain 
(1982)  determined  that  plants  from  the 
most  exposed  site  in  New  Zealand  more 
closely  resembled  those  in  California  than 
those  in  the  other  populations  in  New 

As  Macrocystis  plants  grow  through 
the  water  column,  they  have  fewer  shading 
interactions  with  progressively  fewer 
species.  Pearse  and  Hines  (1979)  found, 
for  example,  that  many  species  of  large 
brown  algae  recruited  into  an  area  near 
Santa  Cruz,  California  recently  cleared  of 
sea  urchins.   Macrocystis  recruited  at 

4-5/m2,  Laminaria  setchel 1 i  i  at  4-12/m2, 
Pterygophora  californica  at  4-6/m2, 
Nereocystis  at  1-2/m2,  and  Cystoseira  at 
1/m2.  Macrocystis  eventually  grew  to  the 
surface,  forming  a  canopy,  while  the 
species  that  were  shaded  below  declined  in 

If  effects  among  species  decrease  in 
importance  once  plants  reach  the  surface 
canopy,  intraspecific  events  must  assume 
more  importance.  Dense  stands,  about  4 
plants/10  m2 ,  provide  a  "forest"  effect, 
with  deep  shading  beneath  the  canopy  (see 
cover  photo).  Darwin  (1860)  remarked  on 
the  calming  effect  which  dense  stands  of 
Macrocystis  have  on  turbulent  inshore 
waters.  This  reduced  flow  can  also  affect 
carbon  assimilation  and  nutrient  uptake 
(see  Section  2.6).  At  the  other  extreme 
of  density,  solitary  plants  do  not  usually 
fare  well.  They  may  be  ravaged  by 
herbivorous  fishes,  especially  halfmoon 
and  opaleye,  which  appear  to  be  attracted 
in  numbers  to  isolated  plants  (North  and 
Hubbs  1968,  LOSL  1983).  Because  the  frond 
meristem  is  at  the  tip,  it  is  easily 
damaged  by  fish  grazing,  and  once 
destroyed,  frond  growth  stops.  These 
plants  may  also  be  more  susceptible  to  the 
effects  of  severe  water  motion  without  the 
dampening  effect  of  nearby  plants. 
Between  these  extremes,  the  effects  of 
density  on  Macrocystis  are  equivocal. 
North's  (1971b)  observation  of  plants  at 
three  densities  showed  that  those  in  the 
densest  stands  (some  15  stipes/m2,  and  7 
stipes/m2)  could  grow  faster  than  those  at 
1/m2.  He  attributed  this  difference  to 
some  unknown  localized  factor  affecting 
growth.  Neushul  and  Harger  (in  press) 
planted  adult  Macrocystis  plants  at 
different  densities  and  found  that,  over  a 
period  of  one  year,  the  number  of  fronds 
per  plant  increased  for  plants  growing  at 
low  density,  stayed  about  the  same  for 
those  at  the  medium  density,  and  decreased 
for  those  at  high  density.  These 
differences  were  also  reflected  in  the 
weights  of  plants,  with  those  at  the 
highest  density  weighing  the  least  (see 
also  Section  5.5.2). 

The  effects  of  density  on  algal 
growth  are  far  from  resolved,  however,  and 
may  be  of  some  importance  to  the  dynamic 
relationships  of  plants  in  kelp 
communities  (c.f.  Schiel  and  Choat  1980). 


It  remains  unclear  whether  sites  which 
naturally  feature  dense  stands  of  kelp  are 
simply  environmentally  favorable,  while 
sites  with  fewer  plants  reflect  less 
favorable  conditions.  The  alternative  is 
that  the  density  of  the  plants  themselves 
modifies  the  site.  Of  course,  both  of 
these  are  possibilities  in  particular 
circumstances,  but  they  are  relevant  to 
attempts  at  establishing  kelp  in  areas 
where  it  is  now  absent.  Other  species  that  form 
surface  canopies  in  California  and  Mexico. 

Nereocystis  luetkeana  (Figure  3)  may  occur 
in  both  pure  and  mixed  stands  with 
Macrocystis  in  that  area  of  California 
where  their  ranges  overlap  (Yellin  et  al. 
1977).  Most  of  the  work  on  this  species, 
however,  has  been  done  north  of  Santa 
Cruz,  California,  where  it  is  the  dominant 
kelp  which  forms  a  surface  canopy.  This 
species  is  an  annual,  and  may  form  dense 
stands  to  a  depth  of  %  12  m  in  central 
California  (Foster  1982a).  Nereocystis 
usually  occurs  in  more  turbulent  water 
than  Macrocystis ,  and  Foster  (1982a)  and 
Van  Blaricom  [Tn  press)  suggested  from 
their  observations  that  bull  kelp 
populations  may  also  be  less  affected  by 
sea  urchin  grazing. 

Duggins  (1980)  found  that  when  dense 
aggregations  of  sea  urchins  were  removed 
in  Torch  Bay,  Alaska,  a  dense  stand  of 
Nereocystis  quickly  recruited.  This 
species  is  an  annual,  however,  and  was 
eventually  replaced  by  perennial 
laminarians.  Nevertheless,  dense  stands 
of  Nereocystis  occur  year  after  year  in 
large  areas  of  inshore  waters,  indicating 
its  ability  to  maintain  space  through 
reseeding  areas  occupied  by  adult  plants 
(Duggins  1980,  Foster  1982a). 

Inshore  areas  from  the  low  intertidal 
to  a  few  meters  depth  are  often  inhabited 
by  dense  stands  of  Egregia  menziesii 
(Figure  3),  a  species  that  can  overlap  in 
depth  distribution  with  Macrocystis 
integrifol  ia,  but  does  not  usually  extend 
into  deep  enough  waters  to  affect  the 
abundance  or  distribution  of  M.  pyrifera. 
Black  (1974)  did  a  demographic  study  of  E. 
menziesi  i  in  the  intertidal  zone  near 
Santa  Barbara,  from  recruitment  to 
senescence.  He  found  that  the  grazing 
activities  and  the  scars  formed  by  the 

limpet  Notoacmea  insessa  were  a  major 
cause  of  frond  breakage,  and  that  the  life 
histories  of  these  two  species  were 
intimately  associated  (Black  1974). 

The  outer  edges  of  some  kelp  forests 
in  southern  California  are  inhabited  by 
the  elk  kelp  Pelagophycus  porra  (Figure  3, 
Plate  ID).  Because  it  occurs  in  deep 
water  (18+  m)  and  is  not  generally 
abundant,  there  is  little  known  of  its 
biology.  In  a  recent  study,  Hart  (1982) 
found  that  stipe  elongation  was  density- 
dependent.  Plants  in  a  10  m2  area  at 
1.4/m2  grew  significantly  faster  than 
those  in  a  10  m2  area  at  0.25  plants/m2. 
Plant  blades  were  significantly  larger, 
however,  in  the  less  dense  stand.  Studies 
by  Parker  and  Bleck  (1966)  and  Coyer  and 
Zaugg-Haglund  (1982)  indicate  that  this 
species  is  an  annual . 

Pelagophycus  may  be  found  at  depths 
to  30  m.  Haptera  are  usually  attached  to 
rock,  but  may  spread  to  sand  and  gravel. 
A  population  at  Big  Fisherman's  Cove, 
Catalina  Island  grows  entirely  on  a  sand 
substratum.  Stipes  may  reach  lengths  of 
27  m,  while  the  blades  of  mature 
sporophytes  may  be  up  to  20  m  long  and  a 
meter  broad  (Abbott  and  Hollenberg  1976). 
This  species  may  have  been  more  abundant 
in  the  past;  drifting  plants  were  commonly 
used  as  a  navigational  aid  to  Spanish  and 
Portugese  mariners  in  the  1600' s, 
signalling  a  change  in  a  ship's  course 
before  land  was  sighted  (Dawson  and  Foster 

Cystoseira  osmundacea  (Figure  1)  is  a 
perennial  species  in  the  Fucales  that 
cohabits  inshore  areas  with  Macrocystis 
plants.  A  study  in  the  Point  Cabrillo, 
Monterey  kelp  forest  (Schiel  in  press  a) 
showed  that  single  plants  6-9  m  deep  could 
have  30+  fronds  extending  to  the  surface. 
Although  the  plants  are  perennial,  the 
reproductive  tissues  and  vegetative 
structures  which  accompany  them  are  highly 
seasonal,  appearing  at  the  surface  of  the 
sea  between  June  and  September.  After 
reproduction,  these  structures  deteriorate 
and  break  away,  leaving  the  holdfast  and 
larger  basal  blades.  In  mid-summer 
densities  of  9  plants/m2  may  produce  an 
estimated  20%  of  the  surface  canopy  in  a 
forest  shared  with  Macrocystis. 
Cystoseira  osmundacea  is  depth-restricted, 


however,  in  its  abundance  and  in  the  sizes 
of  plants.  Below  depths  of  ^  10  m,  plant 
numbers  become  lower,  and  a  decreasing 
proportion  have  thai  1 i  that  extend  more 
than  a  few  meters  from  the  bottom.  This 
sort  of  depth  distribution  is  similar  to 
that  found  for  most  of  the  abundant 
Fucales  found  in  austral  areas  (Schiel 
1981,  Choat  and  Schiel  1982). 

Sargassum  muticum  is  another  Fucales 
that  co-occurs  with  Macrocystis  in  some 
areas  of  southern  California,  especially 
Catalina  Island.  An  experiment  by  Ambrose 
and  Nelson  (1982)  at  Santa  Catalina  Island 
indicated  that  a  dense  recruitment  of  S_. 
muticum  can  preempt  the  space  for  other 
species  to  settle  and  grow,  and  this 
species  may  be  able  to  keep  Macrocystis 
from  localized  sites. 

Sargassum  muticum  has  caused  some 
excitement  since  '  its  accidental 
introduction  and  dramatic  spread  along  the 
west  coast  of  North  America,  and  its 
recent  arrival  on  the  south  coast  of 
England  (Fletcher  and  Fletcher  1975, 
Norton  1977).  Deysher  and  Norton  (1982) 
found  experimentally  that  the  majority  of 
recruits  appeared  within  2-3  m  of  parent 
plants,  although  some  recruits  could  be 
found  at  distances  to  30  m.  It  was 
proposed  that  this  species  may  have  spread 
long  distances  by  detachment  of  vegetative 
fronds  which  continue  to  grow  and  develop 
while  adrift  and  swept  along  by  wind  and 
currents  (Deysher  and  Norton  1982).  As 
this  species  is  monoecious  and 
self-fertile,  populations  could  become 
established  at  considerable  distances  by 
propagules  dispersed  from  one  adult  plant.  Surface  canopy  species  in 
other  areas.  Alaria  f istulosa  is  a  large 
kelp  that  is  particularly  abundant  in 
Alaska.  This  species  has  a  short  stipe 
with  sporophylls  concentrated  near  the 
bottom  of  each  plant.  The  vegetative 
blade,  however,  has  a  gas-filled  mid-rib, 
and  may  reach  a  length  of  25  m  and  a  width 
of  2  m.  At  most  localities,  this  species 
is  largely  confined  to  depths  of  <  5  m. 
Dayton  (1975)  did  selective  canopy 
removals  of  A.  fistulosa,  species  of 
Laminaria  and  Agarum  cribosum  at  a  site 
near  Amchitka  Island,  Alaska.  He  found 
that  when  Laminaria  spp.  were  removed  from 
quadrats  at  5-m  depths,  the  quadrats  were 

colonized  by  Alaria,  but  that  this  species 
did  not  invade  other  quadrats  where  the 
Laminaria  canopy  was  left  intact.  At 
depths  of  9.1  m  and  16.8  m,  Alaria 
colonized  only  the  quadrats  from  which 
both  Laminaria  and  Agarum  were  removed. 
As  few  Alaria  were  found  naturally  at 
these  depths,  Dayton  (1975)  concluded  that 
this  is  a  fugitive  species,  which  may  take 
advantage  of  free  space  but  which  is 
normally  prevented  from  doing  so  by  the 
presence  of  other  species.  He  concluded 
that  the  lower  distribution  of  Alaria 
appeared  to  be  restricted  primarily  by  the 
grazing  activities  of  sea  urchins. 

4.3.3  Understory  Canopy  Species:  Kelp 
Beds  Species  in  California  and 
Mexico.  Many  members  of  the  Laminariales 
and  Fucales  form  a  canopy  0.5  to  2.5  m  off 
the  bottom,  and  dense  stands  of  single 
species  may  completely  or  partially 
exclude  other  species  of  large  brown  algae 
(see  Section  2.4).  Pterygophora 
cal ifornica  (Figure  3,  Plate  IE)  is  a 
perennial  species  abundant  along  the  west 
coast  (Abbott  and  Hollenberg  1976).  This 
species  can  grow  to  maturity  in  6  months 
in  central  California  (Foster  pers.  obs.). 
At  sites  in  Stillwater  Cove,  Carmel  Bay, 
sporophylls  and  terminal  blades  may  be 
almost  entirely  removed  during  periods  of 
intense  water  motion  in  winter.  New 
growth  of  fronds  occurs  in  spring  and,  by 
summer,  frond  growth  is  great  enough  that 
plants  at  4-8/m2  can  form  a  closed  canopy 
over  the  substratum.  This  species  has 
been  transplanted  to  the  Pendleton 
Artificial  Reef  near  San  Onofre  in 
southern  California  (LOSL  1983).  It  was 
believed  to  be  more  resistant  to  fish 
grazing  (thicker  blades,  meristem  at  base 
of  blade)  than  Macrocystis,  and  that  it 
would  modify  the  populations  of  encrusting 
organisms  prevalent  on  the  reef  so  that 
other  brown  algae  might  naturally 
establish.  Storms  and  fish  grazing, 
however,  removed  almost  all  blades  after 
transplantation  (LOSL  1983). 

Growth  rings  and  sporophyll  scars 
have  been  used  to  estimate  the  age  of 
individual  plants  thought  to  live  over  15 
years  (Frye  1918).  Although  Frye's  data 
are  indecipherable,  field  studies  by 
DeWreede  (1984)  and  Reed  and  Foster  (pers. 


obs.)  now  suggest  that  growth  rings  are 
annual .  Maximum  ages  for  Pterygophora 
plants  have  been  estimated  to  be  18  years 
in  central  California  (Reed  and  Foster 
1984),  11  years  in  southern  California 
(Dayton  et  al .  1984),  and  10  years  in 
British  Columbia  (DeWreede  1984). 

All  of  the  understory  kelp  species 
have  been  described  morphologically,  but 
little  is  known  about  most  of  them  from 
field  studies  on  the  west  coast.  Each  may 
form  dense  aggregations  locally,  but  their 
individual  effects  on  the  remainder  of  the 
community  are  generally  not  known.  Some 
of  these  species  can  have  a  fairly  long 
(80+  cm),  erect  stipe,  placing  the  blades 
and  canopy  over  a  meter  above  the 
substratum  (for  example,  Laminaria 
setchelli  i  [Figure  3],  Pterygophora 
cal  ifornica,  and  Eisenia  arborea  [Figure 
3  J ) .  Many  others  have  short  stipes  and 
long  blades.  This  type  of  morphology 
results  in  plants  being  draped  over  the 
substratum  and  flopping  back  and  forth 
with  water  motion.  Laminaria  farlowii , 
Agarum  f imbriatum,  and  Costaria  costata 
are  examples.  Besides  shading  substrata 
near  plants,  abrasion  by  blades  could  also 
have  local  effects.  Dayton  et  al.  (1984) 
calculated  life  tables  for  some  understory 
species  in  southern  California.  They 
estimated  that  Eisenia  arborea  plants  can 
live  for  11  years  and  Laminaria  farlowii 
for  6  years.  By  selectively  removing  the 
understory  kelps,  they  found  that  the 
stipitate  species  (Eisenia,  L_.  setchell  i 
and  Pterygophora)  inhibited  the  successful 
recruitment  of  Macrocystis,  Pterygophora, 
Nereocystis,  and  Desmarestia. 

Extreme  water  motion  may  be  the 
primary  cause  of  adult  Pterygophora 
cal ifornica  mortality  in  central 
California,  as  drift  plants  are  commonly 
observed  on  beaches  after  storms.  At  more 
protected  locations  such  as  Stillwater 
Cove  (see  Section  3.3.1)  other  factors 
such  as  occasional  damage  to  the  meristem 
by  turban  snails  (Section,  or 
destruction  of  the  medulla  in  the  stipe  by 
burrowing  amphipods  (Foster  pers.  obs.) 
may  cause  a  slow  attrition  of  old 
individual s.  Species  in  other  areas. 
There  has  been  extensive  research  on  the 
biology  of  Laminariales  in  many  areas  of 

the  world.  We  will  not  review  that  work 
here,  but  will  mention  a  few  species  that 
have  either  been  well-studied  in  the 
field,  or  whose  effects  on  other  species 
have  been  demonstrated.  Kain  (1979) 
provides  a  review  of  the  biology  and  field 
research  on  Laminaria  and  related  species. 

Various  species  of  Laminaria  and 
Agarum  have  been  studied  in  northern  areas 
of  the  eastern  Pacific.  Demographic 
studies  on  these  species  are  lacking,  but 
some  studies  have  selectively  removed 
canopies  or  have  prevented  sea  urchins 
from  access  to  areas  of  substratum.  Paine 
and  Vadas  (1969)  reported  that  Nereocystis 
became  the  dominant  alga  in  the  first  year 
on  subtidal  rocks  kept  free  of  sea 
urchins,  forming  some  90%  of  the  biomass. 
In  the  following  year,  L_.  groenlandica 
became  the  dominant  alga. 

Dayton  (1975)  worked  with  three 
species  of  Laminaria  and  Agarum  cribosum 
in  Alaska.  Laminaria  longipes  was  able  to 
re-establish  in  areas  after  its  canopy  was 
removed.  It  has  a  rhizome-like  holdfast 
with  multiple  meristems,  and  can  quickly 
regrow  stipes  and  fronds  after  they  are 
removed.  When  the  canopies  of  three 
laminarian  species,  I.  groenlandica ,  I. 
dentigera,  and  I.  yezoensis,  were  removed 
in  a  shallow  site,  the  percentage  cover 
and  density  of  Agarum  increased.  The 
long-term  consequences  of  these  invasions 
were  not  known. 

Duggins  (1980)  removed  Laminaria 
groenlandica  from  several  small  plots  in 
Torch  Bay,  Alaska.  In  the  first  year 
after  removal,  there  was  a  high 
recruitment  of  annual  kelp.  By  the  second 
year,  however,  Laminaria  was  once  again 
dominant  (mean  ±  S.D.:  53  +  27  plants/m2 
vs.  8  ±  7/m2  for  other  species).  There 
was  no  successful  recruitment  of  any 
species  in  the  control  plot  where  the 
canopy  was  left  intact. 

Understory  Laminariales  and  Fucales 
are  very  abundant  in  many  other  boreal  and 
temperate  areas  of  the  world.  In  northern 
New  Zealand,  for  example,  Fucales  are 
usually  dominant  in  shallow  subtidal  areas 
(<  5  m  depth),  while  a  single  kelp, 
Ecklonia  radiata,  dominates  deeper  areas. 
In  most  cases,  the  substratum  beneath 
dense  stands  of  these  algae  is  covered 


with  encrusting  red  algae  (Choat  and 
Schiel  1982).  Removal  of  the  dominant 
canopies  of  one  species  often  allows  the 
invasion  of  another  species.  The  result 
depends  partially  on  the  season  of  the 
year  in  which  canopies  are  removed,  as  the 
peaks  of  fertility  for  individual  species 
are  different  (Schiel  1981). 

Nova  Scotia  is  another  area  which  has 
had  large  research  programs  in  kelp  bed 
ecology.  The  perennial  alga  Laminaria 
longicruris,  may  form  extensive  stands 
from  shallow  depths  to  below  20  m  (Mann 
1972a).  The  extent  of  many  of  these 
stands  has  been  altered  by  sea  urchins 
( Strongy 1 ocentrotus  droebachiensis)  in 
recent  years  (Breen  and  Mann  1976).  The 
biology  and  growth  of  I.  longicruris  have 
been  extensively  studied.  The  growth 
rates  of  this  species  can  be  limited 
during  part  of  the  year  by  low  nutrient 
availability  (Chapman  and  Craigie  1977). 
Gerard  and  Mann  (1979)  found  that  the 
morphology  of  plants  was  influenced  by  the 
intensity  of  water  motion,  and  was 
different  at  exposed  and  sheltered  sites. 
Growth  in  the  exposed  population  was  lower 
than  in  the  sheltered  one  during  8  months 
of  the  year  due  to  low  nutrient  and  light 
levels.  Gagne  et  al.  (1982)  reported  that 
the  potentially  limiting  factors  of  light 
and  nutrients  had  different  levels  at 
various  sites.  Growth  rates  of  plants  may 
therefore  be  different  at  these  sites. 
Where  nutrients  are  plentiful,  maximum 
growth  can  occur  during  summer  when  light 
levels  are  high.  In  nutrient-limited 
areas,  plants  tend  to  concentrate  their 
growth  during  winter  when  nutrient  levels 
are  higher. 

Chapman  (1984)  examined  the 
reproduction,  recruitment  and  mortality  of 
Laminaria  longicruris  and  Laminaria 
digitata  in  a  series  of  innovative 
experiments.  By  measuring  sorus  area  and 
microscopically  examining  sorus  tissue,  he 
estimated  the  number  of  spores  produced  by 
plants  of  both  species.  The  recruitment 
rate  of  each  species  was  estimated  by 
placing  ceramic  bricks  beneath  each  canopy 
during  each  month  of  one  year.  At  the  end 
of  each  month,  bricks  were  brought  into 
the  laboratory  and  placed  under  lights  in 
running  seawater  until  plants  were 
visible.  Natural  recruitment  rates  were 
monitored  in  the  field.   Chapman  (1984) 

found  that:  (1)  J.,  longicruris  produced 
about  9  x  109  spores/m2/yr  and  I.  digitata 
20  x  109  spores/m2/yr;  (2)  the  recruit- 
ment of  microscopic  plants  was  nearly  9  x 
106  recruits/m2/yr  for  I.  longicruris  and 
1  x  106/m2/yr  for  J_.  digitata;  (Tj~  the 
chances  of  survival  from  microscopic  to 
visible  size  was  1  in  9  million  for  J_. 
longicruris  and  1  in  0.5  million  for  L_. 
digitata;  and  (4)  once  plants  were 
visible  in  the  field,  1  in  4  survived  to  a 
year  for  J.,  longicruris  and  1  in  2  for  J_. 
digitata.  The  greatest  mortality, 
therefore,  occurred  between  the  time  when 
microscopic  spores  reached  the  substratum 
and  when  sporophytes  became  visible. 
Adult  plants  lived  up  to  25  months  for  i. 
longicruris  and  42  months  for  _L.  digitata. 

In  the  British  Isles  and  northern 
Europe,  several  species  of  Laminaria  are 
abundant  subtidally.  Laminaria  hyperborea 
is  perhaps  the  most  prominent  and 
important  of  these  species  (Kain  1979). 
Kain  (1975,  1976)  found  that  L.  digitata, 
which  has  a  flexible  stipe,  was  more 
tolerant  to  wave  action  than  was  I. 
hyperborea.  In  calmer  subtidal  sites, 
however,  U.  hyperborea  eventually  appeared 
to  become  dominant  where  both  species  had 
recruited.  In  deeper  water,  this  species 
may  compete  with  J^.  saccharina.  Much 
research  has  been  done  on  J_.  hyperborea. 
It  extends  from  the  low  intertidal  to  20+ 
m  in  depth.  Kain  (1979)  concluded  that 
its  presence  can  be  limited  by  available 
substratum,  grazing,  and  irradiance.  The 
ages  of  plants  varied  between  populations, 
but  based  on  the  presence  of  annual  growth 
rings,  U  hyperborea  plants  could  live  up 
to  13  years  (Kain  1963). 

For  European  Laminaria  spp.,  the 
maximum  growth  of  blades  occurs  in  late 
spring.  Adult  sporophytes  of  I. 
hyperborea,  (those  over  one  year  old 
LLuning  1969]) ,  usually  stop  growth  during 
June  (Kain  1976).  Luning  (1979)  stated 
that  adult  sporophytes  of  i.  digitata  and 
J^.  saccharina  continue  to  grow  during  the 
second  half  of  the  year,  but  at  a  reduced 
rate.  He  concluded  that  photoperiodism 
may  be  important  to  the  regulation  of 
seasonal  growth  for  these  species. 

Laminaria  pal lida  and  Ecklonia  maxima 
both  occur  in  shallow  water  in  South 
Africa,  with  L..  pal  1  ida  dominant  below  ^  8 


m  depth  (Velimirov  et  al.  1977,  Dieckmann 
1980).  Ecklonia  maxima  can  create  bare 
substrata  by  the  sweeping  motion  of  blades 
on  a  long  and  flexible  stipe  (Velimirov 
and  Griffiths  1979).  Dieckmann  (1980) 
found  that  the  growth  rate  of  L.  pal  1 ida 
followed  a  seasonal  cycle,  with  the 
highest  rate  in  early  summer  and  the 
lowest  in  winter.  He  also  found  that 
plants  at  a  deeper  station  (14  m)  had 
lower  growth  rates  than  those  at  8-m 
depth.  He  estimated  that  this  species  may 
1 ive  9+  years. 

Some  of  the  longer-bladed 
Laminariales  from  Japan  can  form  surface 
canopies  in  shallow  water.  Species  of 
Laminaria  and  Undaria  are  also  extensively 
cultivated  (Hasegawa  and  Sanbonsuga  1972). 
The  biology  of  these  species  is  well  known 
(Saito  1972),  but  there  is  little 
information  on  field  populations. 

4.3.4  Bottom  Canopy  Species  Fleshy  and  filamentous 
species.  There  are  hundreds  of  species  of 
fleshy  and  filamentous  algae  found  in  kelp 
forests,  but  only  the  more  common  species 
for  which  we  have  some  ecological 
information  will  be  discussed  and 
illustrated.  Dawson  et  al.  (1960) 
described  many  species;  North  (1971a) 
provided  a  list  of  those  most  common  in 
southern  and  Baja  California,  Mexico, 
while  Devinny  and  Kirkwood  (1974),  Pearse 
and  Lowry  (1974),  Foster  et  al .  (1979a), 
and  Abbott  and  Hollenberg  (1976)  listed 
species  from  central  California. 

There  are  several  studies  from 
California  that  show  some  of  the  effects 
of  overstory  plants  on  bottom  canopy 
species,  and  also  the  effect  of  these 
bottom  canopy  species  on  the  recruitment 
of  other  species.  Kastendiek  (1982)  found 
at  Santa  Catalina  Island  that  the  red  alga 
Pterocladia  capil lacea  was  abundant  under 
a  canopy  of  Eisenia.  If  this  canopy  was 
removed,  the  fucoid  Halidrys  dioica  was 
able  to  spread  adventitiously  and  exclude 
Pterocladia.  Pterocladia  could  flourish 
outside  of  canopies  if  Hal idrys  was 
prevented  from  preempting  space. 
Pterocladia  capillacea  appeared  in  this 
case  to  act  as  a  refuge  species,  occupying 
substrata  under  canopies  of  Eisenia  where 
Hal idrys  could  not  flourish. 

Several  studies  by  Foster  and  his 
co-workers  in  California  have  paid 
particular  attention  to  bottom  canopy 
species  as  important  members  of  kelp 
communities  (Foster  1982a).  Foster 
(1975a)  placed  these  species  into  three 
groups  for  a  study  at  Santa  Cruz  Island 
(Figure  16).  Ephemerals  included  species 
such  as  the  brown  alga  Colpomenia  that 
rapidly  colonized  free  space,  but  were 
seasonal  in  their  appearance  and 
disappearance.  Perennials  with  rapid 
growth  included  the  reds  Pterosiphonia 
dendroidea  and  Rhodymenia  cal ifornica 
(Figure  17),  which  were  seasonal  in  their 
colonization  of  space,  but  could  persist 
through  time.  Perennials  with  slow  growth 
included  Gi gar tin a  spp.  (Figure  17),  and 
the  corallines  (Plate  IF),  which  were  very 
slow  to  colonize  space,  but  could  persist 
for  several  years.  Colonization  by  these 
species  varied  with  season,  with  most 
having  either  a  spring-summer  or  autumn- 
winter  period  of  maximum  reproduction 
(Figure  16).  Foster  (1975b)  found  that 
the  presence  of  an  overstory  could  reduce 
algal  diversity  and  the  percentage  cover 
of  species  below. 

Following  the  removal  of  Macrocystis 
canopies  near  Santa  Cruz,  the  annual  brown 
alga  Desmarestia  1 igulata  var.  1 igulata 
(Figure  17)  became  locally  abundant  during 
spring  and  summer  (Cowen  et  al .  1982; 
Foster  1982a).  Reed  and  Foster  (1984) 
also  found  that  this  species  became 
abundant  when  Macrocystis  and  Pterygophora 
canopies  were  removed.  It  was 
particularly  abundant,  however,  in 
treatments  where  the  branches  of 
articulated  coralline  algae  were  also 
removed.  Desmarestia  spp.  may  reach  a  few 
meters  in  length,  but  do  not  have  erect 
stipes  to  hold  fronds  above  the 
substratum.  During  the  summer  months,  the 
canopy  of  this  species  may  completely 
cover  the  bottom  in  some  local  sites, 
particularly  in  areas  where  winter  storms 
have  removed  Macrocystis  and  Nereocystis 
(Foster  1982a,  Cowen  et  al.  1982,  Reed  and 
Foster  1984). 

Other  species  may  also  have  an  annual 
cycle.  The  fleshy  red  algae  Polyneura 
latissima,  Plocamium  cartilagineum, 
Botryoglossum  farlowianum  (Figure  17, 
Plate  2D) ,  and  Phycodrys  setchelli  i  are 
particularly  abundant  during  summer  in 


JUN      JUL      AUG      SEP      OCT 











NOV     DEC 

JAN     FEB     MAR     APR     MAY 




Periods  of  maximum  colonization 
Only  slight  colonization 
Possible  colonization 

Figure  16.  Colonization  times  for  the  more  abundant  algal  species  that 
recruited  to  artificial  substrata  in  a  kelp  forest  at  Santa  Cruz  Island 
(from  Foster  1975a). 

northern  sites  near  Santa  Cruz  (Foster 
1982a),  although  abundance  may  vary  at 
particular  sites  affected  by  local 
environmental  changes  such  as  sand 
movement  (Breda  1982).  Overall,  there 
appears  to  be  a  general  negative 
correlation  between  the  percentage  cover 
of  Macrocystis  canopies  and  the  cover  of 
bottom  canopy  species.  This  may  be  a 
direct  result  of  shading  on  recruitment 
and  growth,  and/or  an  indirect  result  of 
overgrowth  of  these  plants  by  sessile 
invertebrates  when  light  is  low  (Breda 
1982).  A  composite  graph  of  several 
surveys  at  three  localities  in  central 
California  shows  that  at  times  when 
Macrocystis  cover  is  high,  the  cover  of 
foliose  alqae  is  low  (Figure  18). 

1971a,  Foster  1975a,  1982a).  The  two 
species  of  Cal 1 iarthron  (C.  cheilospo- 
roides  and  C.  tuberculosum,  Plate  IF)  are 
the  largest  of  the  articulated  corallines 
along  the  west  coast,  and  may  have  bran- 
ches over  20  cm  in  length  (Abbott  and 
Hollenberg  1976).  These  species,  like 
some  of  the  more  coarse,  fleshy  red  algae 
such  as  Gel idium  robustum  (Figure  17; 
Barilotti  and  Silverthorne  1972),  are 
relatively  slow  growing  and  long-lived. 
Cal 1 iarthron  and  related  plants  can  also 
be  early  colonizers  on  bare  substrata 
(Johansen  and  Austin  1970,  Foster  1975a), 
and  this  genus  appears  to  maintain 
coverage  for  many  years  (Johansen  and 
Austin  1970,  Foster  1975a,  Reed  and  Foster 
1984).  Articulated  corallines.  A 
dense  cover  of  articulated  coralline  algae 
is  common  on  the  bottom  in  many  kelp 
forests  (Johansen  and  Austin  1970,  North 

Reed  and  Foster  (1984)  assessed  the 
effects  of  Calliarthron  on  the  recruitment 
of  other  species.  In  a  site  where 
Macrocystis  and  Pterygophora  canopies  were 





















A    " 



ol   150- 



O  " 





)  " 



a,   100- 



7     50- 










i             i 


Figure  17.  Common  understory  algae  (layer 
2  in  Figures  3  and  6)  found  in  kelp 

0  30  60  90  120 

%    OF   FALL,  1977    Macrocystis    CANOPY    COVER 

Figure  18.  Relationship  between  Macro- 
cystis  canopy  cover  and  upright  (non- 
encrusting)  understory  algal  cover  in 
three  kelp  forests  north  of  Santa  Cruz. 
Total  understory  algal  cover  exceeds  100% 
as  layering  was  determined.  Macrocystis 
canopy  cover  at  each  site  was  considered 
100%  in  fall  1977.  Cover  at  other  times 
is  expressed  as  percent  of  this  value. 
Understory  cover  was  not  surveyed  at  a 
Point  Santa  Cruz  site  in  fall  1977. 

removed,  they  found  that  the  greatest 
recruitment  of  Desmarestia  spp.  and 
Laminariales  was  in  treatments  from  which 
the  branches  of  articulated  corallines 
were  also  removed.  Clearances  to  bare 
rock  aid  not  increase  recruitment  of  other 
species,  suggesting  that  it  is  the 
branches  themselves  that  inhibit 
recruitment.  This  could  be  caused  by 
shading,  by  abrasion,  by  the  presence  of 
sediment  which  may  be  trapped  in  the 
articulated  algae,  or  by  small  grazers 
concealed  in  the  branches. 

Other  articulated  corallines  such  as 
Bossiella  spp.  are  also  common  in  kelp 
communities,  but  little  is  known  of  their 
effects  on  other  species.  It  is  likely, 
however,  that  where  these  calcareous  algae 
are  abundant,  they  also  reduce  recruitment 
of  other  plants,  especially  Macrocystis 
(Wells  1983). 

4.3.5  Encrusting  Species 

Little  is  known  about  the  effects  of 
encrusting  species  in  kelp  communities. 

Encrusting  corallines  (Plate  2A)  of  the 
genera  Lithothamnium  and  Lithophyl lum  are 
extremely  common  in  subtidal  habitats, 
including  Macrocystis  forests  (Abbott  and 
Hollenberg  1976).  TFese  plants  occur  from 
the  intertidal  zone  to  depths  below  100  m 
in  the  subtidal  zone,  and  appear  as  pink 
to  purple  crusts  on  almost  all  surfaces 
not  occupied  by  other  organisms.  One 
species,  Lithophyl lum  grumosum,  may  form 
crusts  up  to  several  millimeters  thick. 
The  encrusting  stages  of  articulated 
corallines  are  sometimes  mistaken  for 
these  species.  Encrusting  corallines  in 
kelp  forests  probably  grow  slowly,  and 
certainly  may  persist  for  long  periods. 
Many  species  of  filamentous  and  foliose 
algae  may  grow  epiphytically  on  them. 
Boulders  covered  by  encrusting  corallines 
are  frequently  inhabited  by  juvenile 
abalone,  and  in  the  laboratory,  encrusting 
corallines  induce  settlement  of  abalone 
larvae  (Morse  et  al.  1979).  On  the  other 
hand,  these  crusts  can  reduce  recruitment 
of  some  sessile  animals  (Breitburg  1984). 


4.3.6  Epiphytes 


Many  species  of  algae  occur 
epiphytically,  some  as  obligates  on  other 
species  of  algae.  Even  though  it  is  an 
annual  ,  Nereocystis  may  have  many 
epiphytes,  the  commonest  of  which  are  the 
reds  Porphyra  nereocystis  and 
Antithamnionella  pacifica,  and  the  green 
Enteromorpha  linza  (Abbott  and  Hollenberg 
1976) .  P.  nereocystis  and  A.  pacifica  may 
be  found  on  the  stipes  of  plants,  while  E. 
linza  is  usually  found  at  the  lower 
junctions  of  fronds.  Microcladia 
cal ifornica  is  commonly  found  on  Egregia 
menziesi i  in  the  low  intertidal,  while  M. 
coul teri  (Figure  17)  occurs  on  many 
species  of  red  algae  as  well  as  on  large 
brown  algae  (Abbott  and  Hollenberg  1976). 

During  the  summer,  species  of  the 
brown  alga  Coilodesme  may  be  found 
abundantly  on  Cystoseira.  Coilodesme 
cal ifornica  is  particularly  abundant  on  _C. 
osmundacea.  Diatoms  (see  Section  4.2.1 
above)  and  many  other  algal  species  such 
as  Myriogramme  caespitosa,  Pterochondria 
woodii ,  and  Microcladia  coul teri  may  occur 
on  Macrocystis  and  other  kelps. 

Epiphytic  algae  seem  to  become 
particularly  abundant  as  fronds  senesce. 
This  is  probably  not  due  to  the  epiphytes 
actually  overwhelming  plants  and  causing 
their  demise,  but  to  the  general 
deterioration  of  host  plants  at  this  time. 
Fil ion-Myklebust  and  Norton  (1981) 
reported  that  the  intertidal  brown  seaweed 
Ascophyl Turn  nodosum  sheds  its  epidermis, 
which  may  remove  epiphytes.  Moss  (1982) 
found  that  continuous  shedding  of  the 
outermost  layers  of  meristoderm  cell  walls 
occurred  in  the  perennial  alga  Hal idrys 
sil  iquosa,  and  suggested  that  this  might 
be  a  general  occurrence  in  the  Fucales. 
These  sorts  of  events  may  be  especially 
important  for  long-lived  perennial 
species,  which  have  a  longer  exposure  to 
potential  epiphytes.  It  has  also  been 
suggested  that  the  abundant  small 
Crustacea  that  inhabit  the  fronds  of  large 
brown  algae  may  benefit  plants  by  removing 
epiphytes  (Schiel  and  Choat  1980). 
Limpets  that  live  on  the  surface  of  stipes 
may  provide  similar  benefits  (Dayton  et 
al.  1984).  Most  of  these  ideas  have  yet 
to  be  tested. 

4.4.1  Introduction 

Giant  kelp  forests  are  inhabited  by 
an  abundant  and  species-rich  invertebrate 
fauna  found  in  a  variety  of  habitats 
(Figure  6).  In  giant  kelp  holdfasts 
alone,  Andrews  (1945)  found  over  23,000 
individuals  representing  nine  phyla  in 
five  holdfast  collections  from  the 
Monterey,  California  area  (exact  size  of 
collections  unspecified).  McLean  (1962) 
identified  204  species  of  invertebrates 
seen  during  30  SCUBA  dives  in  a  primarily 
Nereocystis  luetkeana  forest  south  of 
Monterey  ("site  described  in  Chapter  3). 
Pequegnat  (1964)  found  over  300  species  on 
a  shallow  rocky  reef  in  southern 
California.  The  diversity  of  sizes, 
morphologies,  feeding  types,  and  behaviors 
is  also  high,  making  even  an  overview  of 
conspicuous  species  and  their  ecology  a 
difficult  task. 

Unfortunately,  there  is  no  single 
reference  equivalent  to  that  for  the  algae 
by  Abbott  and  Hollenberg  (1976)  describing 
subtidal  marine  invertebrates  in 
California.  However,  because  many  species 
range  into  the  low  intertidal  zone,  the 
recent  intertidal  survey  by  Morris  et  al . 
(1980)  is  very  helpful,  as  are  Ricketts  et 
al.  (1968),  and  for  central  California, 
Smith  and  Carlton  (1975).  These  books,  as 
well  as  MacGinitie  and  MacGinitie  (1968), 
also  include  natural  history  information. 
Popular  books  (North  1976a,  Gotshall  and 
Laurent  1979)  summarize  information  on  the 
more  common  subtidal  invertebrates  likely 
to  be  found  in  giant  kelp  forests.  We 
will  discuss  some  of  these  below, 
particularly  species  that  are  common,  and 
for  which  there  is  some  ecological 

We  have  organized  groups  of 
invertebrates  functionally  by  feeding 
type,  rather  than  taxonomically ,  in  an 
attempt  at  ecological  relevance.  Feeding 
type  distinctions,  however,  are  often 
unclear  as  a  particular  species  such  as 
the  sea  urchin  Strongylocentrotus 
franciscanus  may  graze  attached  plants 
(grazer) ,  catch  drift  (detritus  feeder), 
consume  animals  (predator),  and  perhaps 
use  dissolved  organic  matter  (DOM).  Where 


there  is  such  overlap,  we  have  put  the 
animal  in  what  appears  to  be  the  most 
common  or  notorious  feeding  type. 

4.4.2  Filter,  Suspension,  and  Detritus 
Feeders  Sponges  (Porifera). 
Sponges,  along  with  tunicates  and 
bryozoans,  are  probably  the  most  common 
sessile  animals  in  kelp  forests, 
particularly  on  steeply  sloping  walls  and 
in  deeper  water  (Plate  2C).  North  (1971b) 
listed  41  species  of  sponges  in  southern 
California-Baja  California  kelp  forests, 
with  encrusting  Haliclona  spp.  ,  vase-like 
Leucil la  (=  Rhabdodermel la)  nuttingi ,  and 
the  large,  spherical,  orange  Tethya 
aurantia  (Figure  19)  the  most  common.  In 
central  California,  Pearse  and  Lowry 
(1974)  mentioned  22  species  from  the  Point 
Cabrillo  kelp  forest  near  Monterey,  and 
McLean  (1962)  11  species  from  Granite 
Creek  south  of  Carmel  ,  California. 
Species  are  generally  similar  in  both 
central  and  southern  California.  The 
cobalt  sponge  Hymenamphiastra  cyanocrypta 
(Plate  2B)  is  particularly  abundant  as 
encrusting  sheets  on  vertical  walls  and 
under  ledges  from  Monterey  south  in 
central  California  kelp  forests.  The  deep 
blue  color  is  derived  from  a  symbiotic 

Pachycenathis  iimbnaius 

Figure  19.  Invertebrate  filter,  suspen- 
sion, and  detritus  feeders  common  in  kelp 

blue-green  alga  living  in  its  tissue 
(Morris  et  al.  1980).  Many  sponges  are 
important  in  the  diets  of  nudibranchs,  and 
the  top  shell  Cal 1 iostoma  annulatum  feeds 
on  T.  aurantTa  (Gotshall  and  Laurent 
1979J.  Cnidarians  (Cnidaria).  Hy- 
droids,  sea  anemones,  solitary  (cup)  cor- 
als, hydrocorals,  and  gorgonians  are  ubi- 
quitous members  of  the  kelp  forest  sessile 
animal  assemblage.  The  hydroids  Abietin- 
aria  sp.  and  Aglaophenia  spp.  are  common, 
and  along  with  other  species,  are  often 
early  colonists  of  new  substrata.  Many 
hydroids  are  preyed  upon  by  nudibranchs 
(Morris  et  al .  1980). 

Six  genera  of  sea  anemones  commonly 
occur  in  kelp  forests,  with  the  large, 
solitary  Tealia  spp.  (Figure  19), 
Anthopleura  xanthogrammica,  and  especially 
in  deeper  water,  Metridium  senile,  locally 
abundant.  The  most  conspicuous  and 
abundant  species  is  the  strawberry 
"anemone"  (not  a  true  anemone)  Corynactis 
californica.  Colonies  of  this  animal  may 
completely  cover  vertical  walls,  and  the 
orange  to  red  bodies  with  white,  club- 
shaped  tentacles,  are  visually  striking 
(Plate  2E).  In  addition  to  the  above 
species,  the  tube-dwelling  Pachycerianthus 
fimbriatus  (Figure  19)  is  frequent  in  sand 
patches  within  and  along  ^e  outer  edge  of 
kelp  forests.  All  of  these  anemones  feed 
on  almost  any  animal  tissue  or  detritus  of 
appropriate  size  that  comes  within  reach 
of  thei  r  tentacles. 

Anemones,  like  other  cnidarians,  have 
stinging  structures  (nematocysts) ,  and 
when  the  animals  are  aggregated  (e.g., 
Corynactis  cal ifornica) ,  may  constitute  a 
barrier  to  mobile  benthic  animals  such  as 
sea  stars.  Sea  star  prey  such  as 
gastropods  may  thus  have  a  refuge  from 
predators  when  surrounded  by  anemones  or 
corals  (Herri  inger  1983).  However,  the 
leather  star  Dermasterias  imbricata  feeds 
on  C.  cal ifornica  (Rosenthal  and  Chess 

Three  species  of  cup  corals, 
Balanophyllia  elegans  (Plate  2B),  Para- 
cyathus  stearnsii ,  and  Astrangia 
lajol laensis  occur  in  giant  kelp  forests. 
The  bright  orange  EL  elegans  is  most 
common,  often  growing  with  Corynactis 


cal ifornica  throughout  the  range  of 
Macrocystis.  B.  elegans  has  nonpelagic 
planulae,  and  studies  by  Gerrodette  (1981) 
indicated  dispersal  distance  is  less  than 
0.5  m  from  the  parent,  perhaps  accounting 
for  the  usually  aggregated  distribution  of 
the  species.  Fadlallah  (1983)  estimated 
an  average  lifespan  of  6-11  years  for  this 
coral  at  Point  Cabrillo  in  central 
California,  with  mortality  resulting  from 
overgrowth  of  young  corals  by  other 
sessile  animals  and  from  predation  by 
spider  crabs. 

The  hydrocoral  Al  lopora  cal  ifornica 
(Plate  2F)  usually  occurs  in  deep  water  at 
the  outer  edge  of  kelp  forests  or  on 
offshore  pinnacles.  Currents  are  stronger 
and  the  water  cleaner  in  such  habitats, 
perhaps  providing  reduced  sedimentation 
and  necessary  food  (Gotshall  and  Laurent 
1979).  Van  Blaricom  (pers.  comm. )  has 
observed  A.  cal  ifornica  at  depths  less 
than  10  m  within  a  giant  kelp  forest  where 
currents  were  strong  and  the  water  clear. 
Ostarello  (1973)  suggested  sedimentation 
and  competition  with  other  sessile 
organisms  for  space  as  sources  of 
mortality  in  young  colonies,  and  breakage 
and  abrasion  as  important  to  older 
colonies.  An  encrusting  species,  A. 
(=  Stylantheca)  porphyra ,  is  occasionally 
also  found  in  California  kelp  forests. 

A  number  of  large  (to  almost  a  meter 
tall),  fan-shaped  gorgonians  are  frequent 
in  southern  California  kelp  forests  and 
reefs.  Muricea  fructicosa  (Figure  19)  and 
M.  cal ifornica  are  most  common  within  kelp 
stands,  while  the  red  Lophogorgia 
chi lensis  usually  occurs  in  deeper  water. 
All  of  these  feed  on  plankton,  and  usually 
orientate  perpendicular  to  the  prevailing 
currents  or  surge.  M.  cal ifornica  can  be 
aged  from  rings  in  the  base,  and  Grigg 
(1975)  used  age-height  relationships  to 
determine  size-frequency  distributions  in 
various  habitats  near  San  Diego.  These 
distributions,  along  with  habitat  data, 
were  then  used  as  measures  of  habitat 
suitability  and  stability  for  the  species. 
Breakage  from  storms  and  increased 
sedimentation,  burial,  and  abrasion  were 
the  major  causes  of  mortality.  Grigg 
(1975)  suggested  that  increased 
sedimentation  from  sewage  outfalls  led  to 
a  reduction  in  the  number  of  gorgonian 
colonies   at   Palos   Verdes,   an   area 

influenced  by  Los  Angeles  sewage  discharge 
and  where  other  kelp  forest  organisms, 
including  Macrocystis,  have  also  declined 
(see  Chapter  6) .  Bryozoans  (Ectoprocts). 
Bryozoans  are  found  almost  everywhere  in 
kelp  forests,  and  on  everything  from  solid 
rock  walls  to  delicate  algal   fronds. 

Woollacott  and  North  (1971)  listed  59 
species  collected  near  the  bottom  in  six 
geographical  areas  from  Monterey, 
California,  to  southern  Baja  California, 
Mexico.  Ten  of  these  were  considered 
widely  distributed. 

The  encrusting  Lichenopora 
novae-zelandiae,  Membranipora  tuberculata, 
and  M.  membranacea  (Figure  6~)  are 
extremely  common  on  algal  blades, 
especially  those  of  Macrocystis. 
Membranipora  encrustations  may  cover  up  to 
75%  of  the  kelp  blades  at  particular  times 
in  particular  forests,  and  can  grow  to 
cover  a  blade  almost  completely  in  three 
weeks  (Wollacott  and  North  1971).  Wing 
and  Clendenning  (1971)  found  that  blades 
with  nearly  complete  cover  of  bryozoans 
required  50%  higher  light  intensities  for 
growth  than  unencrusted  blades.  Dixon  et 
al.  (1981)  showed  that  plants  near  a 
thermal  outfall  in  southern  California 
were  much  more  encrusted  with  Membranipora 
than  were  plants  in  a  nearby  kelp  forest. 
Experiments  demonstrated  that  blade  loss 
from  Macrocystis  was  correlated  with  the 
degree  of  encrustation,  as  blades  tended 
to  break  off  easily  when  heavily  fouled. 
Predation  on  Membranipora  by  fishes  may 
also  indirectly  cause  blade  loss 
(Wollacott  and  North  1971,  Dixon  et  al . 
1981).  Fouling  may  be  reduced  on  other 
kelps  by  frond  abrasion,  and  this  form  of 
disturbance  can  have  important  effects  on 
the  entire  epifaunal  community  on  kelp 
blades  (Fletcher  and  Day  1983). 

Two  other  bryozoans  are  common  on 
understory  vegetation  and/or  on  the 
bottom:  the  arborescent  Thalamoporella 
cal ifornica,  and  the  lacy,  fan-like 
Phidolopora  pacifica.  The  latter  serves 
as  habitat  for  numerous  small  gastropods 
and  crustaceans.  J.  cal  ifornica  may  have 
a  biomass  close  to  300  g/m2  [wet  weight) 
in  some  kelp  stands,  about  50%  of  the 
total  sessile  animal  biomass  (Wollacott 
and  North  1971). 


Bryozoans  are  commonly  among  the 
first  organisms  to  settle  on  newly  exposed 
substrata  in  kelp  forests,  and  may  remain 
abundant  in  shaded  habitats  or  those 
protected  from  predation  (Foster  1975a, 
b).  Selective  predation  by  the  bat  star, 
Patiria  miniata,  can  alter  succession  in 
the  bryozoan  assemblage  (Day  and  Osman 
1981).  One  species,  Cryptoarachnidium 
(=  Victorella)  argil! a ,  is  a  common  early 
colonizer  on  nearshore  artificial  reefs  in 
southern  California  (Turner  et  al.  1969, 
Grant  et  al .  1982).  This  animal  forms 
encrusting  sheets  composed,  in  part,  of 
consolidated  sediments  and  can  dominate 
reef  surfaces  for  long  periods.  Dominance 
is  probably  maintained  in  the  absence  of 
predators  by  inhibiting  settlement  of  and 
growing  over  other  sessile  species  (LOSL 
1983).  Bryozoans,  and  sessile  animals  in 
general,  appear  capable  of  inhibiting  the 
settlement  and  growth  of  benthic  algae, 
even  in  subtidal  habitats  with  sufficient 
light  for  algal  growth.  Predators 
(particularly  fish  and  sea  stars)  of  these 
sessile  animals  may  mediate  this 
competitive  dominance,  allowing  local 
coexistence  (Foster  1972,  1975b). 

Brittle  stars,  sea  stars, 

sea  cucumbers  and  sea  urchins  (Echinoder- 
mata).  Brittle  stars  are  extremely  abun- 
dant in  kelp  forests.  They  are  not. obvi- 
ous because  they  are  normally  found  out  of 
sight  under  cobbles,  in  holdfasts,  dense 
algal  turfs,  and  other  cryptic  habitats. 
These  animals  generally  feed  by  extending 
their  arms  and  trapping  food  particles 
using  the  sticky  mucous  on  the  spines  and 
podia.  They  are  particularly  active  at 
night,  when  one  can  see  hundreds  of  arms 
sticking  out  in  the  water  among  the 
haptera  of  giant  kelp  holdfasts. 

The  abundance  of  one  of  the  more 
common  brittle  stars,  Ophiothrix  spiculata 
(Figure  19),  ranged  up  to  21 
individuals/100  cm3  in  giant  kelp 
holdfasts  from  southern  California 
(Ghelardi  1971).  Andrews  (1945)  found 
total  brittle  star  densities  of  up  to 
300/m2  of  holdfast  (projected  surface 
area),  with  0.  spiculata  and  Amphipholis 
pugetana  most  abundant.  Unfortunately, 
other  than  occasional  species  lists  and 
abundance  estimates,  little  is  known  of 
the  ecology  of  these  ubiquitous  animals. 

Most  common  sea  stars  in  kelp  forests 
are  predators,  the  exceptions  being  the 
red-orange  Henri ci a  leviuscula  that  traps 
small  food  particles  in  mucous  on  the 
undersides  of  its  arms  (Morris  et  al. 
1980),  and  the  bat  star  Patiria  miniata, 
an  omnivorous  scavenger.  The  latter  is 
discussed  in  more  detail  under  Grazers 

Sea  cucumbers  use  their  tentacles  to 
extract  food  from  sediments  or  water,  and 
only  the  tentacles  of  some  species  can 
normally  be  seen  protruding  from  crevices, 
holes,  or  holdfasts.  Common  species 
include  the  red  Cucumaria  miniata  in 
central  California,  the  small  (2-3  cm) 
orange  Pachythyone  rubra  from  Monterey  to 
southern  California,  and  the  small,  white 
Eupentacta  quinquesemita,  and  large,  brown 
Parastichopus  spp.  (Figure  19)  throughout 
the  range  of  Macrocystis  pyrifera.  P. 
rubra  can  occur  at  densities  of  up  to 
10,000/m2  in  some  areas  at  San  Nicolas 
Island  off  southern  California  (Cowen 
pers.  comm. )  Sea  cucumbers  are  eaten  by 
various  sea  stars  (Morris  et  al .  1980). 

All  species  of  sea  urchins  found  in 
kelp  forests  can  capture  and  feed  on  drift 
algae,  and  this  may  be  their  most  common 
mode  of  feeding.  However,  because  they 
can  graze  attached  plants  (and  are  most 
notorious  for  it),  they  are  discussed 
under  Grazers  below.  Molluscs  (Mollusca).  Numer- 
ous filter-feeding  clams  inhabit  sandy 
areas  in  kelp  forests,  but  the  most  common 
on  hard  substrata  are  the  rock-boring  pho- 
lads  (Family  Pholadidae)  seen  as  siphons 
extending  out  of  short  calcareous  tubes 
above  the  substratum.  The  most  abundant 
of  these  is  Parapholas  californica,  whose 
densities  can  be  over  50/m2  in  kelp 
forests  with  relatively  soft  shale 
bottoms.  Bore  depth  can  be  30  cm,  and 
these  clams  can  cause  considerable  erosion 
of  soft  rock  bottoms  (Morris  et  al.  1980). 
The  sea  star  Pisaster  brevispinus  is 
capable  of  extruding  its  stomach  into 
pholad  burrows  and  digesting  the  clams  in 
place  (Van  Veldhuizin  and  Phillips  1978). 

Mussels  (Mytilus  spp.)  are  most 
common  in  the  intertidal  zone,  but  are 
occasionally  found  in  deep  water  (Chan 
1973,  Paine  1976).  The  size  record  for  M. 


californianus  is  from  a  subtidal  reef 
(Chan  1973).  This  suggests  that  perhaps 
predation,  and  not  the  abiotic  environment 
or  food  availability,  limits  the  abundance 
of  this  genus  in  kelp  forests.  The 
purple-ringed  rock  scallop  Hinnites 
giganteus  (=  H.  mul tirugosus)  is  common  in 
kelp  forests,  occurring  attached  by  one 
valve  to  rock  walls  and  inside  crevices. 
This  species  is  taken  for  food  by  sport 
divers,  and  is  being  investigated  as  a 
possible  candidate  for  mariculture 
(Leighton  and  Phleger  1977).  Two  other 
locally  abundant  bivalves  that  attach  by 
one  valve  are  the  jingle,  Pododesmus 
cepio,  and  Chama  arcana  (=  C.  pel lucida). 
The  latter  can  occur  stacked  up  at 
densities  of  near  300/0.1  m2  on  subtidal 
reefs  (Pequegnat  1964).  The  small  scallop 
Leptopecten  latiauratus  occasionally 
settles  in  large  numbers  on  giant  kelp 
fronds  in  southern  California,  and  may 
cause  the  fronds  to  sink  (Carter  pers. 
comm.).  Bernstein  and  Jung  (1979) 
suggested  that  this  animal,  like  the 
oceanic  barnacle,  is  normally  excluded 
from  kelp  forests  by  predatory  fishes. 

In  addition  to  the  filter  feeding 
molluscs  mentioned  above,  there  are  a  few 
that  capture  particles  in  mucous  nets. 
The  vermetid  Petaloconchus  montereyensis 
grows  in  masses  of  intertwined  calcareous 
tubes,  each  tube  about  2  mm  in  diameter, 
at  densities  of  up  to  100,000  snails/  m2 
(Morris  et  al .  1980).  The  larger  sessile 
snail  Serpulorbis  squamigerus  occurs 
singly  or  in  masses.  Both  species  are 
preyed  upon  by  the  sea  star  Pisaster 
giganteus  (Foster  1975b,  Harrold  1981), 
and  the  former  is  a  major  item  in  the  diet 
of  this  sea  star  in  one  central  California 
kelp  forest  (Harrold  1981). 

Although  only  occasionally  common, 
the  nudibranch  Mel  ibe  leonina  is  of 
interest  because,  unlike  most  of  its 
predatory  relatives,  this  large  nudibranch 
commonly  sits  on  giant  kelp  fronds,  and 
captures  food  from  the  passing  water  in 
its  expanded  oral  hood  (Morris  et  al . 
1980).  Polychaete  worms  (Annelida, 
Polychaeta).  Polychaetes  are  probably 
second  only  to  crustaceans  in  diversity 
and  abundance   in  giant  kelp  forests. 

Polychaetes  occur  in  almost  all  subhabi- 
tats  within  a  kelp  forest.  Normally 
hidden,  they  are  rarely  seen  except  when 
when  samples  are  being  sorted  in  the 
laboratory.  Abundances  are  particularly 
high  in  kelp  holdfasts  (Andrews  1945, 
Ghelardi  1971).  Many  are  probably  preda- 
tors on  other  small  animals. 

Polychaetes  that  are  commonly  visible 
underwater  generally  capture  particles  in 
the  water  with  modified  head  parts  or 
gills  that  project  out  from  tubes,  cracks, 
etc.  on  or  in  the  substratum.  The  most 
common  are  spirorbids,  whose  tiny,  coiled, 
calcareous  tubes  dot  the  surfaces  of  giant 
kelp  blades  and  understory  algae 
(particularly  Rhodymenia  spp.).  Bernstein 
and  Jung  (1979)  found  Spirorbis  spirillum 
most  abundant  in  the  troughs  of 
corrugations  on  older  Macrocystis  blades 
(up  to  3/cm2).  Chemicals  from  the  algae 
apparently  stimulate  spirorbid  larvae  to 
settle  on  particular  species,  and  even 
parts  of  plants  (Morris  et  al.  1980).  The 
sabellid  (feather  duster  worm)  Eudistylia 
polymorpha  is  common  on  the  bottom,  where 
its  colorful  feeding  and  respiratory  plume 
projects  out  of  holes  and  crevices. 

Perhaps  the  most  abundant  large 
polychaete  in  kelp  forests  is  Diopatra 
ornata,  whose  parchment-like  tubes, 
decorated  with  rubble  and  algal  fragments, 
project  above  unconsolidated  substrata. 
Densities  can  be  so  high  that  the  worms 
can  completely  cover  the  bottom.  Sipunculans  (Sipuncula). 
Peanut  worms  are  often  common  in  kelp 
forests,  but  like  the  brittle  stars 
discussed  above,  are  rarely  seen  because 
of  their  cryptic  habits.  They  feed  by 
eating  sediment  and  ingesting  organic 
matter,  or  by  capturing  small  particles. 
Phascolosoma  agassizii  is  probably  most 
common,  and  Andrews  (1945)  found  over  80 
individuals  of  this  species  per  square 
meter  (projected  holdfast  area)  in  giant 
kelp  holdfasts  from  central  California. 
Foster  (pers.  obs.)  found  similar 
densities  in  recent  collections  from  this 
area.  Morris  et  al.  (1980)  indicate  that 
sipunculans  are  preyed  upon  by  gastropods.  Crustaceans  (Arthropoda, 
Crustacea).  Crustaceans  are  certainly  the 
numerically   dominant   animals   in   kelp 


forests,  and  many  feed  on  detritus  and 
plankton.  In  turn,  small  crustaceans  are 
a  major  food  of  many  kelp  forest  fishes 
(Quast  1971d,  Bray  and  Ebeling  1974,  Coyer 
1979,  Laur  and  Ebeling  1983;  see  Section 
4.5  below).  Gammarid  and  caprellid 
amphipods  (Figure  19),  mysids  (Figure  14), 
and  isopods  (e.g.,  Idotea,  Figure  20)  are 
especially  common  on  seaweeds,  and 
low-growing  algal  turfs  containing  high 
densities  of  these  animals  are  common  fish 
feeding  areas,  particularly  for  perches 
(Bray  and  Ebeling  1974,  Laur  and  Ebeling 
1983).  Coyer  (1979)  found  gradients  in 
abundance  and  size  of  particular 
crustaceans  from  the  bottom  to  the  canopy 
on  giant  kelp  plants,  and  suggested  that 
some  size  gradients  may  reflect  size 
selective  predation  by  fishes.  Many  of 
the  small  crustaceans  migrate  from  the 
substratum  into  the  water  at  night. 
These,  along  with  purely  planktonic 
species,  are  discussed  in  Section  4.2.2 

Hermit  crabs,  primarily  the  genus 
Pagurus,  are  frequent  in  kelp  holdfasts 
(Andrews  1945,  Ghelardi  1971),  and  mats  of 
articulated  corallines  and  other  dense 
understory  algae.  They  are  generally 
scavengers  and  eat  considerable  amounts  of 
algae  (Morris  et  al .  1980).  Little  is 
known  of  the  ecology  of  these  animals  in 
kelp  forests,  but  they  may  be  important 
grazers,  particularly  on  small  or  delicate 
plants.   Foster  (pers.   obs.)  observed 

hermit  crabs,  trapped  within  cages  over 
fouling  plates,  completely  remove  a  lush 
growth  of  foliose  algae  in  one  week. 


5cm     Idotea  sp. 

Spider  crabs, 

other  crabs  and  lobsters 

large  Cancer  spp. ,  and 
found  in  kelp 
forests  are  mainly  grazers  or  predators, 
but  all  may  occasionally  feed  on  detritus. 

A  careful  search  of  almost  any 
substratum  in  a  kelp  forest  will  also 
reveal  barnacles.  They  can  completely 
dominate  newly  exposed  surfaces.  Balanus 
crenatus  is  particularly  abundant  in 
central  California,  while  _B.  pacificus  is 
more  common  in  southern  California.  The 
large  (over  10  cm  in  diameter)  Q.  nubilus 
occurs  occasionally  along  the  entire 

of  Balanus 

observe    dense 

crenatus  in  central 

bare  substrata  and  the 

understory  kelps.   They  are 

upon  by  sea  stars  (Pisaster 

Figure  20.   Common  invertebrate  grazers  in 
kelp  forests. 




stipes  of 

often  fed 

spp.)  that  will  even  ascend  stipes  to 
feed.  Hurley  (1975)  found  that  flatworms 
were  major  predators  on  subtidal  ]3. 
pacificus.  Sheephead  (Semicossyphus 
pulcher;  see  Section  4.5  below)  also  eat 
barnacles  in  southern  California  (Cowen 
1983),  particularly  on  newly  placed 
artificial  reefs  where  other  prey  may  be 
less  abundant  (Carter,  pers.  comm.).  The 
oceanic  barnacle  Lepas  pacif ica  may  be 
excluded  from  kelp  forests  by  fish 
predation  (Bernstein  and  Jung  1979).  Tunicates  (Urochordata, 
Ascidiacea).  Tunicates  are  extremely 
abundant  in  kelp  forests,  forming  multi- 
colored coverings  on  walls  and  other 
shaded  areas.  The  solitary  Styela  mon- 
tereyensis  (Figure  19)  is  particularly 
common,  and  often  mixed  with  understory 
algae.  Rosenthal  et  al.  (1974)  observed 
S.  montereyensis  being  eaten  by  the  sea 
stars  Pisaster  giganteus  and  Astrometis 
sertulifera,  and  the  whelk  Kelletia 
kelletii . 

Among  the  many  colonial  species 
(Plate  2C),  the  lobed,  grey-pink 
Cystodytes  lobatus  is  abundant,  and  may 
occur  to  depths  of  200  m  (Morris  et  al . 
1980).  This  and  other  tunicates  often 
provide  habitat  for  small  worms, 
crustaceans  and  clams,  and  are  common  prey 


At  the  various  stages  of  their  life 
cycles,  seaweeds  in  giant  kelp  forests 
fall  prey  to  different  species  of 
herbivorous  invertebrates.  Plants, 
however,  may  grow  too  large  to  be  consumed 
by  particular  grazers,  so  that  the  number 
of  grazing  species  that  may  actually 
remove  entire  plants  decreases  as  plants 
get  larger.  There  are  only  a  few  species 
of  grazers  that  directly  remove  adult 
plants,  but  many  species  live  on  the 
plants,  feed  upon  their  tissues,  and 
indirectly  cause  the  removal  of  all  or 
parts  of  the  plants.  These  indirect 
effects  include  grazing  of  plant  tissue, 
which  may  provide  centers  for  fungal  and 
bacterial  infections  that  can  sever 
blades,  fronds,  or  holdfasts;  this 
severing  can  provide  sites  for  epiphyte 
growth  or  can  weaken  parts  of  the  plants, 
rendering  them  vulnerable  to  removal  by 
increased  water  motion  or  entanglement 
with  other  plants. 

This  section  discusses  the  more 
common  species  of  invertebrates  known  to 
have  direct  or  indirect  effects  on  the 
removal  of  seaweeds,  particularly  kelps 
(Table  6).  There  are  many  more  herbivores 
present  in  Macrocystis  forests  than  will 
be  mentioned  or  listed  here.  More 
comprehensive  species  lists  can  be  found 
in  Leighton  (1971),  Smith  and  Carlton 
(1975),  and  Morris  et  al .  (1980).  Sea  urchins  and  sea  stars 

(Echinodermata).  Sea  urchins  are 
generally  the  most  obvious  grazers,  and 
may  significantly  affect  the  distribution 
and  abundance  of  macroscopic  algae.  Their 
extensive  grazing  effects  have  been 
recorded  in  tropical,  temperate  and  boreal 
regions  (Lawrence  1975).  There  has  been 
extensive  local  removal  of  plants  by  sea 
urchins  in  some  Macrocystis  pyrif era 
forests  in  southern  California  (Leighton 

1971;  see  also  Chapters  3  and  5),  and  kelp 
distribution  increased  after  sea  urchins 
declined  at  one  site  in  central  California 
(Pearse  and  Hines  1979). 

In  most  kelp  forests,  there  are  often 
great  numbers  of  sea  urchins,  but  these 
commonly  have  little  effect  on  attached 
kelp  (Lowry  and  Pearse  1973,  Foster  1975a, 
Cowen  et  al .  1982),  feeding  mostly  on 
drift  material  (Mattison  et  al .  1977, 
Vadas  1977,  Duggins  1980,  Harrold  and  Reed 
in  press).  Extensive  feeding  by  sea 
urchins  on  attached  plants  appears  to  be 
related  to  the  dispersion  of  individuals 
and  their  density  on  patches  of  substratum 
(e.g.,  Schiel  1982),  and  to  behavioral 
changes  associated  with  the  availability 
of  drift  algae  (Dean  et  al.  1984,  Harrold 
and  Reed  in  press),  or  even  large  zoo- 
plankton  (Duggins  1981a). 

There  is  a  general  pattern  for  cases 
where  patches  of  kelp  are  completely 
removed  by  sea  urchins.  Dense 
aggregations  of  animals  converge,  and  a 
"feeding  front"  is  formed.  The  urchins  in 
the  vanguard  of  movement  are  often  large 
individuals,  tightly  packed  together 
(Leighton  1971,  Dean  et  al.  1984).  Most 
or  all  of  the  plants  in  the  path  of  these 
dense  aggregations  are  consumed  or  else 
detached  from  the  substratum  by  grazing 
through  the  holdfasts  or  lower  fronds. 
Sea  urchins  further  back  in  the 
aggregations  feed  on  this  newly-freed 
plant  material . 

Large-scale  removal  of  Macrocysti s  on 
the  west  coast  has  been  primarily  by  two 
species,  Strongylocentrotus  franciscanus 
(Plate  2D),  and  the  smaller  j>.  purpuratus. 
Another  species,  the  white  urchin 
Lytechinus  anamesus,  may  occasionally 
graze  large  kelp  (Clarke  and  Neushul  1967) 
but  is  probably  more  important  as  a  grazer 
of  juveniles  (Dean  et  al .  1984). 

The  large  red  sea  urchin 
Strongyl ocentrotus  franciscanus  occurs  on 
rocky  substrata  throughout  the  range  of 
Macrocystis  on  the  west  coast  (Morris  et 
<TL  1980).  Leighton  (1971)  described 
large  individuals  of  this  species  forming 
the  advancing  edge  of  a  feeding  front  that 
removed  a  large  tract  of  Macrocystis 
(^  100  x  200  m)  in  the  Point  Loma  kelp 
forest  during  1960  (see  Table  7).   The 


Table  6.   Common  invertebrate  grazers 
affect  recruitment.   Common  names  are 

which  may  remove  tissue  from  kelp  plants  or 
from  North  (1971b)  and  Morris  et  al .  (1980). 


Common  name 

Grazing  effects 

Strongyl ocentrotus 

S_.  purpuratus 

Lytechinus  anamesus 


Patiria  miniata 

Hal iotis  rufescens 

H.  fulgens 
H.  corrugata 
Tegula  brunnea 

T.  funebral is 
]_.   pul  1  igo 
T.  eiseni 
T.  montereyi 
]_.   aureotincta 
Norrisia  norrisi 

Red  sea  urchin 
Purple  sea  urchin 
White  sea  urchin 

Bat  star 

Red  abalone 

Green  abalone 
Pink  abalone 
Brown  turban  snail 

Black  turban  snail 
Dusky  turban  snail 
Banded  turban  snail 
Monterey  turban  snail 
Gilded  turban  snail 
Norris' s  top  snail 

Call iostoma  annulatum  Purple-ringed  top 

C.    canal  iculatum 
C.    ligatum 
Astraea  undosa 

A.  gibberosa 
Mitrella  carinata 

Channeled  top  snail 
Blue  top  snail 
Wavy  top  snail 

Red  top  snail 
Carinated  dove  snai 1 

Directly  removes  plants;  consumes  all  parts  of  plants. 

Same  as  above. 

May  graze  juveniles,  and  portions  of  holdfasts  and 
lower  fronds,  weakening  plant  attachment;  southern 
California  to  Baja  only. 

Grazes  drift  plants;  possibly  grazes  holdfasts; 
southern  California  to  Baja  only. 

At  high  densities,  may  graze  microscopic  stages, 
affecting  recruitment  and  early  survivorship. 

Feeds  extensively  on  drift  kelp;  may  graze  attached 
stipes  and  sporophylls. 

Same  as  above. 

Same  as  above. 

Abundant  on  Macrocystis ,  other  kelps,  and  Cystoseira. 
Grazes  surfaces  of  blades  and  fronds;  may  cause 
weakening  of  tissue. 

Same  as  above  but  only  in  low  intertidal. 

Same  as  above. 

Same  as  above. 

Same  as  above. 

Same  as  above. 

Same  as  above. 

Eats  kelp,  but  appears  to  feed  mainly  on  bryozoans 
hydroids,  diatoms,  detritus. 

Same  as  above. 

Same  as  above. 

Found  on  substratum;  may  graze  lower  stipes  and 
sporophyl Is. 

Same  as  above. 

Abundant  on  Macrocystis  blades  and  fronds;  feeds  mainly 
on  detritus. 

Lacuna  unifasciata    Chinkshell 

Feeds  on  stipes,  producing  pits. 


Table  6  Concluded  . 


Common  name 

Grazing  effects 

Megathura  crenulata 

Notoacmea  insessa 

Colli  sell  a  instabilis 


Lepidozoma  cooperi 

Tonicella  lineata 

Cryptochiton  stelleri 

Aplysia  californica 

A.  vaccaria 

Idotea  resecata 

\_.   stenops 
Paracerceis  cordata 

Ampithoe  homeral is 

A.  rubricata 
Cymadusa  uncinata 
Limnoria  algarum 

Pugettia  producta 
Tal  iepus  nuttaVj  i 

Giant  keyhole  limpet   Minimally  effects  kelps;  feeds  on  understory  seaweeds 
and  ascidians. 

Seaweed  limpet       Found  almost  exclusively  on  Egregia  menziesii;  grazes 
fronds  and  causes  severe  weakening. 

Unstable  seaweed      Found  on  stipes  of  Laminaria  spp.  and  Ptery- 
limpet  gophora;  no  evidence  of  damage  to  plants. 

Very  indirect  effects;  may  graze  algal  spores. 
Same  as  above. 

Found  on  encrusting  corallines;  effects  as  above. 
Grazes  on  bottom;  effects  unknown. 

Lined  chiton 

Gumboat  chiton 

California  brown 
sea  hare 

California  black 
sea  hare 

Kelp  isopod 

Kelp  curler 


Kelp  crab 
Southern  kelp  crab 

Occasional   grazing  on  bottom  and  portions  of 
kelp  plants. 

Grazes  on  Egregia;   effects  unknown. 

Found  on  Microcystis  and  Pelagophycus;   eats 
holes   in  blades,   causing  weakening  and  providing 
centers   for   infection. 

Found  on   Egregia. 

May  derive  nourishment  from  kelp,   but  no  visible 

Rolls  and  cements  edges  of  blades  to  form  a  sticky 
web;   likely  feeds  on  blades. 

Same  as  above. 

Same  as  above. 

Burrows  into  holdfasts  and  may  cause 
considerable  weakening. 

Mainly  herbivorous;   eats  kelp  and  other  algae. 
Same  as  above. 

smaller  species,  the  purple  urchin  J5. 
purpuratus,  also  shares  the  west  coast 
distribution  of  Macrocystis.  It  can  reach 
very  high  densities  in  these  feeding 
aggregations,  some  90/m2  in  places 
(Leighton  1971). 

A  relationship  between  the  feeding 
activities  of  species  of  large  and  small 
sea    urchins    was     also     noted    by     Duggins 

(1981b)  in  Torch  Bay,  Alaska.  Large 
Strongylocentrotus  franciscanus  trapped 
drift  plant  material  which  the  smaller 
species,  S_.  droebachiensis,  seemed  unable 
to  hold  down  by  itself.  It  appears  clear 
for  west  coast  Macrocystis  communities, 
however,  that  either  S.  franciscanus  or  S_. 
purpuratus  is  capable  of  extensive  grazing 
on  attached  plants. 



Table  7.   Concentration  and  biomass  of  two  sea  urchin  species  in  1 
samples  taken  at  three  positions  across  grazing  band  (from  Leighton  1971). 

Sample  number 
and  position 

in  numbers 
S.      S. 


fran?  pur 

rr,  b 

j%r    i% 


per  m2 

in  weight 
S.      S. 
fran.  purp. 

j%r    (if 

per  m2 



At  grazing  front    94.0   6.0 

9  m  behind  front    39.0  61.0 

18  m  behind  front   15.0  85.0 



99.3  0.7 
64.0  36.0 
33.5  66.5 

aS.  fran.  =  Strongyl ocentrotus  f ranciscanus , 
^S.  purp.  =  S.  purpuratus. 


The  smaller  white  sea  urchin, 
Lytechinus  anamesus ,  occurs  from  southern 
California  to  Baja  California,  Mexico 
(Morris  et  al.  1980).  The  species  feeds 
extensively  on  smaller  algae,  particularly 
foliose  reds,  and  its  grazing  effects  on 
large  kelp  are  generally  much  less  than 
that  of  red  and  purple  sea  urchins. 
Clarke  and  Neushul  (1967)  and  Dean  et  al . 
(1984)  reported  that  high  densities  of 
Lytechinus  anamesus  may  remove  adult 
_  by  " 

Macrocystis  plants  by  grazing 
holdfasts  and  lower  fronds. 


Another  sea  urchin,  the  diadematid 
Centrostephanus  coronatus,  may  eat  kelp 
(Vance  1979) ,  producing  very  localized 
effects;  however,  it  is  not  an  aggregating 
species,  and  its  distribution  is  normally 
not  extensive  in  kelp  communities,  except 
at  some  of  the  Channel  Islands  and  islands 
offshore  of  Baja  California,  Mexico. 

The  bat  star  Patiria  miniata  (Figure 
20)  may  affect  algal  recruitment  by 
digesting  spores  and  small  plants  when  it 
everts  its  stomach  over  the  substratum. 
It  is  found  in  abundance  on  rocky 
substrata  (4-5  individuals/m2  in  many 
places)  throughout  the  range  of  giant 
kelp.  Bat  stars  are  omnivores  and 
scavengers,  and  also  eat  tunicates  and 

other  encrusting  animals.  The  polychaete 
worm  Ophiodromus  pugettensis  commonly 
occurs  as  a  commensal  on  the  sea  star's 
oral  surface.  Molluscs  (Mollusca).  Many 
species  of  molluscs  feed  on  kelp  forest 
plants.  Particularly  prominent  are  the 
abundant  turban  and  top  snails  (Table  6). 
It  would  be  unusual  for  the  grazing 
activities  of  these  molluscs  to  result  in 
the  removal  of  adult  plants.  They  can, 
however,  damage  fronds  and  blades, 
resulting  in  the  severing  of  these  parts 
from  adult  plants.  Tegula  spp.  in  Carmel 
Bay,  when  particularly  abundant  (^  20 
individuals  per  plant),  has  been  observed 
to  retard  or  prevent  the  growth  of  new 
sporophylls  on  Pterygophora  cal ifornica 
during  spring  months.  If  storms  remove 
most  large  fronds  from  Macrocystis ,  these 
snails  can  remove  the  remaining  fronds  and 
thus  kill  the  entire  plant  (Schiel  and 
Foster  in  prep.).  Riedman  et  al .  (1981) 
and  Watanabe  (1984a)  recorded  that  the 
abundances  of  three  species  of  Tegula  were 
stratified  with  depth  in  a  Macrocystis 
forest  near  Pacific  Grove,  central 
California.  Tegula  brunnea  (Figure  20) 
was  the  most  abundant  turban  snail  in 
shallow  water  (-4  m  depth),  while  T. 


pul ligo  was  more  abundant  in  deeper  areas 
(-11  m),  There  was  little  overlap  in 
their  distribution.  The  third  species,  T. 
montereyi ,  was  the  least  abundant  of  the 
three  turban  snails,  and  tended  to  be  most 
common  at  ^  6  m  depth.  In  addition  to 
living  and  feeding  on  large  brown  algae, 
these  species  can  be  found  at  densities  of 
^  40/m2  on  the  substratum  (Watanabe 
1984a).  Here,  they  may  also  graze  small 
plants  and  spores. 

Many  other  grazing  gastropods  are 
present  in  Macrocystis  forests;  their 
habits  and  effects  are  largely  unknown. 
Several  species  of  Cal liostoma  (Plate  IF) 
can  be  found  on  kelp  plants.  They  are 
omnivores  eating  sessile  animals  as  well 
as  kelp  (Morris  et  al .  1980),  but  their 
effects  on  kelp  tissue  are  probably 
minimal.  Mitre  11  a  carinata  and  Lacuna 
unifasciata  are  both  small  species,  and 
can  be  the  most  abundant  gastropods  found 
on  Macrocystis  plants  (Leighton  1971, 
Morris  et  al .  1980).  Their  grazing 
effects  are  also  probably  minimal. 
Norrisia  norrisi  (Figure  20)  and  species 
of  Astraea  can  be  abundant  in  kelp 
forests,  particularly  on  the  fronds  of 
Macrocystis  and  Eisenia  (Schmitt  et  al . 
1983).  NT"  norrisi  feed  on  sporophylls, 
stipes  and  young  fronds,  and  Leighton 
(1971)  reported  that  stipe  breakage  may 
result  from  this  grazing.  The  giant 
keyhole  limpet  (Megathura  crenulata)  and 
several  species  of  chitons  may  graze  algal 
spores  from  the  substratum,  but  no 
significant  effects  on  kelp  have  been 
reported.  Ton  ice!  la  lineata  (Plate  2A)  is 
often  abundant  on  encrusting  corallines  in 
central  California  kelp  forests,  and  may 
be  responsible  for  keeping  areas  free  of 
other  algae. 

The  California  brown  sea  hare, 
Aplysia  californica,  may  be  locally  common 
in  kelp  forest  and  grazes  on  a  variety  of 
algae  (Morris  et  al.  1980).  We  have  seen 
mating  aggregations  of  this  species  in 
kelp  forests  in  Carmel  Bay.  During 
periods  of  calm  water,  individuals  can 
occasionally  be  found  in  the  tops  of 
Pterygophora  cal ifornica,  grazing  on  the 
blades.  A.  vaccaria,  the  California  black 
sea  hare  is  most  common  in  southern 
California  and  Baja  California,  Mexico. 
This  species  may  be  the  world's  largest 
gastropod,  with  individuals  over  0.5  m 

long  and  weighing  nearly  16  kg.  Egregia 
is  reported  as  its  primary  food  (Morris  et 
al.  1980). 

Several  species  of  abalone  live  in 
kelp  forests,  and  all  consume  many  species 
of  algae.  The  red  abalone  (Hal iotis 
rufescens;  Figure  20),  the  green  abalone 
~{IL  fulgens) ,  and  the  pink  abalone  (H_. 
corrugata)  were  important  species  in  sport 
and  commercial  fisheries  but,  recently, 
the  harvest  of  the  primarily  intertidal 
black  abalone  (_H.  cracherodii )  has 
increased,  probably  because  of  the  impacts 
of  commercial  and  sport  fishing  on  the 
former  species  (see  Section 
Hines  and  Pearse  (1982)  report  that 
abalone  populations  within  a  kelp  forest 
foraged  by  sea  otters  exhibit  high 
recruitment,  growth  rates,  and  turnover 
rates.  Abalone  feed  extensively  on 
Macrocystis  (Leighton  1971,  Tegner  and 
Levin  1982).  This  is  almost  entirely 
drift  material,  however,  captured  by  the 
animals  with  their  powerful  feet.  Species 
of  Hal iotis  have  little  effect  on  attached 
plants.  Crustaceans  (Arthropoda, 
Crustacea).  The  kelp  isopod  Idotea  (= 
Pentidotea)  resecata  (Figure  20)  dwells  on 
the  upper  fronds  and  blades  of  Macro- 
cystis, and  can  heavily  graze  the  blades 
(Jones  1971).  North  (1966)  reported  that 
this  feeding  activity  once  extensively 
damaged  the  canopy  of  Macrocystis  in  a 
wide  area  of  the  Point  Loma  kelp  forest. 
The  holes  in  blades  resulting  from  their 
grazing  may  also  be  sites  for  fungal  and 
bacterial  infections.  Another  isopod,  the 
pillbug  Paracerceis  cordata,  probably 
causes  little  damage  to  kelp  plants. 

The  gribble  Limnoria  (=  Phyco- 
limnoria)  algarum  may  occasionally  cause 
adult  Macrocystis  to  be  detached  from  the 
substratum.  This  isopod  can  be  abundant 
in  Macrocystis  holdfasts  (Andrews  1945). 
It  burrows  into  the  haptera,  forming 
tunnels  which  may  severely  weaken  the 
holdfasts  (Jones  1971).  Increased  water 
motion  may  then  dislodge  these  plants.  A 
related  isopod  can  cause  considerable 
weakening  of  giant  kelp  holdfasts  in 
Argentina  (see  Section  3.3.3). 

The  kelp  curling  amphipods  Ampithoe 
humeralis,  A.   rubricata,  and  Cymadusa 


uncinata  build  tubes  in  kelp  laminae  by 
curling  the  edges  of  blades  and  sticking 
them  together.  They  eat  kelp,  and  may 
puncture  blades  with  their  spines  and 
hooks  (North  and  Schaefer  1964). 

Other  crustaceans  known  to  feed  on 
kelp  forest  seaweeds  are  various  spider 
crabs  (Hines  1982),  especially  Taliepus 
nutal  li ,  and  the  kelp  crab  Pugettia 
producta  (Figure  20).  Although  often 
abundant,  their  grazing  does  not  appear  to 
have  a  great  effect  on  plants. 

4.4.4  Predators 

Many    species 
invertebrates    inhabit 
Macrocystis  forests,  but 
is  known  about  their 
dynamic  relationships  of 
kelp  stands.   Table  8 

of  predatory 
or  frequent 
overal 1 ,  little 
effects  on  the 
organisms  within 
lists  the  more 

common  or  larger  predators  found  in  kelp 
forests  on  the  west  coast  of  North 
America.  This  list  includes  only  a  small 
subset  of  species  that  may  be  found  in 
many  localities.  More  comprehensive  lists 
can  be  found  in  Ricketts  et  al .  (1968), 
North  (1971b),  Smith  and  Carlton  (1975), 
and  Morris  et  al.  (1980).  Sea  stars  (Echinodermata). 
Several  species  of  predatory  sea  stars  may 
be  easily  located  in  most  kelp  forests. 
The  larger  species  (see  Table  8)  can  be 
voracious  predators  of  other  invertebrate 
species,  especially  favoring  sea  urchins, 
gastropods,  and  chitons.  Intertidally, 
sea  stars  of  the  genus  Pisaster  may 
directly  affect  the  species  composition 
and  may  allow  successional  events  in  some 
communities  (Paine  1974).  They  may 
preferentially  consume  mussels,  the 
competitively  dominant  species  on  some 

Table  8.  Common  invertebrate  predators  found  in  Macrocystis  forests. 


Common  name1 

Leather  star 



Astrometis  sertul if era 
Pisaster  ochraceus    Ochre  star 
£.  giganteus 
P_.   brevispinus 


Patiria  miniata 

Navanax  inermis 

cal ifornica 

Loligo  opalescens 

Sunflower  star 

Bat  star 

Common  squid,  sea 
avian,  calamari 

Predatory  effects 

Will   eat  the  purple  sea  urchin  S.   purpuratus, 
anemones,  and  corals. 

Occasionally  feeds  on  chitons  and  sea  urchins. 

Eats  snails,  limpets,  chitons,  and  barnacles. 

Same  as  above. 

Same  as  above. 

Commonly  eats  sea  urchins,  snails,  chitons, 
crabs,  and  other  sea  stars. 

May  eat  smal 1  Lytechinus  anemesus. 

Eats  other  opi sthobranchs. 

Will  eat  Navanax,  anemones,  and  other  members 
of  its  own  species. 

Feeds  mainly  on  shrimp-like  crustaceans. 


Table  8  Concluded . 


Common  name 

Octopus  bimaculoides   Two-spotted  octopus 

0.  rubescens 

Octopus  dofleini 

Red  octopus 

North  Pacific 
giant  octopus 

0.  micropyrsus 

Cypraea  spadicea      Chestnut  cowrie 
Amphissa  columbiana    Wrinkled  dove  snail 
Conus  californicus    California  cone 


Panul irus  interrruptus  California  spiny 


Loxorhynchus  grandis   Sheep  crab 

L_.  crispatus         Moss,  masking  crab 

Pelia  tumida         Dwarf  crab 

Cancer  antennarius    Rock  crab 

C.   anthonyi 
C_.  jordani 
C.   productus 

Yel low  crab 
Hairy  cancer  crab 
Red  crab 

Lophopanopeus  bel lus 

bellus  Black-clawed  crab 

Predatory  effects 

Feeds  mainly  on  molluscs  (limpets,  abalone, 
other  gastropods)  and  crustaceans  (e.g.,  crabs). 

Same  as  above. 

Same  as  above. 

Found  in  kelp  holdfasts;  feeds  on  small 
molluscs  and  crustaceans. 

Feeds  on  snails'  eggs,  anemones,  ascidians. 

Common  in  kelp  holdfasts;  little  known. 

Feeds  on  gastropods,  bivalves,  polychaetes 
and  others. 

Feeds  on  a  wide  variety  of  invertebrates. 

Feeds  on  molluscs  and  echinoderms. 

Feeds  on  a  variety  of  invertebrates. 

Common  in  kelp  holdfasts;  feeds  on  a 
variety  of  small  invertebrates. 

Common  around  bases  of  kelp  plants;  eats  a 
variety  of  invertebrate  prey. 

Eats  a  variety  of  invertebrate  prey. 

Common  in  kelp  holdfasts;  unknown  feeding. 

Eats  a  variety  of  invertebrate  prey. 

Common  in  kelp  holdfasts. 

a  From  North  (1971b)  and  Morris  et  al .  (1980), 

shores  of  the  Pacific  northwest.  Because 
of  their  effects,  they  have  been  called 
"keystone  species"  (Paine  1966).  It  has 
also  been  recorded  that  the  sudden 
intrusion  of  sea  stars  in  tidepools  will 
cause  the  rapid  exit  of  sea  urchins,  which 
may  eventually  allow  many  species  of  large 
algae  to  colonize  (Paine  and  Vadas  1969). 
The  indirect  effects  of  sea  stars  on  algal 
assemblages  in  subtidal  habitats,  however, 
are  less  certain. 

The  large  sunflower  star  Pycnopodia 
helianthoides  (Figure  21)  commonly 
consumes  sea  urchins.  Duggins  (1983) 
found  that  predation  of  sea  urchins  by 
this  starfish  in  Torch  Bay,  Alaska  can 
create  short-lived  patches  free  of 
herbivores,  which  may  significantly  affect 
subtidal  algal  assemblages.  P_. 
hel  ianthoides  will  also  eat  chitons, 
gastropods,  crabs,  and  other  sea  stars. 
Pisaster  spp.  (Figure  21)  have  a  similar 




Figure  21.   Some  common  invertebrate  pre- 
dators in  kelp  forests. 

broad  diet  (over  40  prey  items  for  P_. 
giganteus  in  a  central  California  kelp 
forest  LHarrold  1981]  and  34  in  southern 
California  [Rosenthal  1971]),  as  does 
Astrometis  sertul ifera.  However,  the 
latter  are  less  effective  than  Pycnopodia 
at  capturing  large  sea  urchins.  The 
leather  star  Dermasterias  imbricata 
(Figure  21)  will  eat  the  smaller  purple 
sea  urchin  Strongylocentrotus  purpuratus 
(Rosenthal  and  Chess  1972)  as  well  as  the 
anemones  Corynactis  cal ifornica, 
Anthopleura  xanthogrammica ,  A. 
elegantissima  and  Metridium  senile  (Annett 
and  Pierotti  1984).  Sebens  (1983) 
indicated  that  predation  by  Dermasterias 
and  shading  by  algae  may  prevent 
Anthopleura  spp.  from  occupying  subtidal 
habitats.  Schmitt  (1982)  found  that  sea 
stars  and  other  predators  affected  the 
distribution  of  Tegula  spp.  on  subtidal 
reefs  at  Catalina  Island.  In  the  Point 
Cabrillo  kelp  forest  in  central 
California,  sea  star  and  fish  predation 
limits  T.  brunnea  to  shallow  water  where 
understory  vegetation  provides  a  partial 
refuge  from  these  predators  (Watanabe 

Schroeter  et  al .  (1983)  found  that 
the  bat  star  Patiria  miniata  could  affect 
the  distribution  of  the  small  white  sea 
urchin  Lytechinus  anamesus  on  a  small 
scale  in  a  kelp  stand  near  San  Onofre  (San 
Diego  County).  Patiria  could  capture  and 
consume  Lytechinus  in  experiments  done  in 

the  laboratory.  From  the  escape  response 
of  Lytechinus  noted  in  the  laboratory, 
these  workers  concluded  that  the  small- 
scale  distribution  of  the  species  in  the 
kelp  forest  was  the  result  of  the 
predatory  activities  of  Patiria. 
Preferential  feeding  on  particular 
bryozoans  by  Patiria  also  affects 
succession  in  bryozoan  assemblages  (Day 
and  Osman  1981).  Molluscs  (Mollusca). 
Several  species  of  octopus  are  found  with- 
in kelp  forests.  They  feed  on  a  wide 
variety  of  animals,  but  mostly  on  gastro- 
pods and  crabs.  Schmitt  (1982)  indicated 
that  predation  by  Octopus  bimaculatus  and 
other  animals  can  have  important  effects 
on  the  distribution  of  Tegula  spp.  at 
Catalina  Island.  0.  bimaculatus  also  prey 
on  Norrisia  norrisi .  Moreover,  if  this 
snail  is  only  damaged  by  0.  bimaculatus , 
subsequent  fouling  by  barnacles  on  the 
damaged  shell  makes  the  snail  less  able  to 
cling  to  kelp  plants,  and  reduces  its 
ability  to  escape  from  other  benthic 
predators  such  as  sea  stars  (Schmitt  et 
al.  1983).  Some  species  of  octopus  are 
large  and  can  even  capture  and  consume 
large  abalone.  The  cryptic  coloring  and 
reclusive  nature  of  octopuses  render  them 
difficult  to  observe  in  their  natural 

The  common  squid  Lol igo  opalescens  is 
an  infrequent  visitor  to  kelp  habitats. 
It  feeds  mainly  on  euphausids  and  other 
shrimp-like  crustaceans. 

Many  species  of  nudibranchs  are 
commonly  seen  in  kelp  forests.  The 
opisthobranchs  include  some  quite  colorful 
species,  and  provide  a  striking  contrast 
to  the  often  drab  surroundings  of  their 
benthic  habitats.  They  feed  on  sponges, 
anemones,  hydroids,  and  other 
opisthobranchs.  We  have  listed  only  two 
large  species,  Navanax  inermis  and 
Pleurobranchia  cal ifornica  (Table  8) . 

Predatory  prosobranch  gastropods  are 
abundant  in  kelp  forests,  particularly 
around  giant  kelp  holdfasts.  The  chestnut 
cowrie  Cypraea  spadicea  feeds  on 
gastropods,  ascidians,  and  anemones. 
Conus  cal ifornicus,  the  California  cone, 
eats  bivalves,  polychaetes,  gastropods, 
and  various  other  small  animals  (Morris  et 


al.  1980).  The  whelk,  Kelletia  kelletii, 
is  a  carnivorous  scavenger  with  a  diet 
similar  to  Pisaster  giganteus.  Rosenthal 
(1971)  found,  from  observations  made  off 
San  Diego,  that  these  two  species  often 
converge  on  the  same  food  source  and  feed 
together,  even  though  P_,  giganteus 
occasionally  eats  J<.  kelletii .  The  miter 
Mitrae  idae  can  be  common  in  kelp  forests 
and  feeds  on  sipunculans  (Fukuyama  and 
Nybakken  1983).  Little  is  known  about  the 
wrinkled  dove  snail  Amphissa  columbiana, 
which  is  particularly  common  in  holdfasts 
of  Macrocystis  (Andrews  1945).  Crustaceans  (Arthropoda, 
Crustacea).  The  spiny  lobster  Panulirus 
interruptus  (Figure  21)  has  been  found  as 
far  north  as  Monterey  Bay,  but  is  common 
only  south  of  Point  Conception.  It  was 
once  more  abundant  than  it  is  today  (see 
Chapter  6),  but  continual  removal  of  this 
food  species  by  commercial  fishermen  and 
recreational  divers  has  reduced  its 
numbers.  Panulirus  feeds  on  a  wide 
variety  of  invertebrates,  and  Tegner  and 
Dayton  (1981)  and  Tegner  and  Levin  (1983) 
suggested  that  it  may  be  an  important 
predator  of  sea  urchins. 

The  last  group  of  predatory 
invertebrates  which  we  will  mention  is  the 
true  crabs,  whose  members  are  abundant  in 
kelp  forests.  Several  of  the  species 
listed  in  Table  8  are  common  in  or  around 
Macrocystis  holdfasts.  Species  of  Cancer 
(Figure  2~T)  and  Loxorhynchus  are  larger 
crabs  which  feed  on  various  invertebrates. 
The  dwarf  crab  Pelia  tumida  and  the 
xanthid  crab  Lophopanopeus  be! lus  bel lus 
are  commonly  found  in  kelp  holdfasts 
(Andrews  1945),  but  little  is  known  about 
their  feeding  habits. 

4.5  FISH 

4.5.1  Introduction 

As  is  true  of  most  other  organisms 
discussed  in  this  chapter,  almost  all 
species  of  fish  found  in  kelp  forests  can 
also  be  found  on  subtidal  reefs  devoid  of 
surface  canopy  kelps,  and  fishes  common  in 
kelp  forests  are  among  the  first  to 
colonize  newly  placed  artificial  reefs 
with  almost  no  macroalgae  (Turner  et  al. 
1969,  Grant  et  al.  1982,  LOSL  1983).  The 
heterogeneous   kelp   forest   environment 

does,  however,  provide  an  important  source 
of  food  and  shelter  for  many  fishes.  As 
many  as  125  species  have  been  reported  to 
inhabit  rocky  reefs  and  kelp  forests  off 
southern  California  (Feder  et  al.  1974). 
Quast  (1971a)  listed  57  species  associated 
with  kelp  forests  in  southern  California; 
Burge  and  Schultz  (1973)  reported  77 
species  from  the  Diablo  Cove  area  near  San 
Luis  Obispo,  and  Miller  and  Geibel  (1973) 
identified  67  species  between  San  Simeon 
and  Monterey.  Detailed  descriptions  of 
these  species  can  be  found  in  the  above 
references  or  in  popular  books  such  as 
Fitch  (1971,  1975),  Gotshall  (1981),  and 
Eschmeyer  et  al.  (1983).  Choat  (1982) 
provides  an  excellent  review  of  the 
ecological  consequences  of  fish  feeding  in 
temperate  waters.  The  more  common  fishes 
frequently  found  in  kelp  forests  are 
discussed  below  and  many  are  illustrated 
in  Figure  22. 

There  are  a  number  of  differences  in 
kelp  forest  fish  assemblages  between 
central  and  southern  California,  and  these 
have  been  largely  attributed  to  differ- 
ences in  water  characteristics.  In 
particular,  southern  California  waters  are 
generally  less  turbid,  less  turbulent,  and 
warmer.  Tropically-derived  species  or 
families  are  much  more  prevalent  there, 
and  include  the  Clinidae  (clinids), 
Gobiidae  (gobies),  Pomacentridae  (damsel- 
fishes),  the  Labridae  (wrasses),  the 
Serranidae  (basses),  and  the  Kyphosidae 
(sea  chubs)  (Ebeling  et  al.  1980a,  b). 
Temperate  families  include  the  Embio- 
tocidae  (surfperches) ,  the  Scorpaenidae 
(rockfishes) ,  the  Hexagrammidae  (green- 
lings),  and  the  Cottidae  (sculpins) 
(Ebeling  et  al.  1980a,  b).  Waters  of 
central  California  have  fewer  tropically 
derived  species  and  fewer  families,  but 
generally  more  species  per  family, 
particularly  of  rockfishes. 

Even  though  both  temperate  kelp 
forests  and  tropical  reefs  occur  at 
similar  depths  and  have  diverse  fish 
assemblages,  the  behaviors  of  the  fishes 
in  the  two  habitats  are  different.  The 
tropics  are  characterized  by  a  daily  shift 
in  activity  between  diurnal  and  nocturnal 
species  that  may  be  a  result  of  changes  in 
the  presence  of  predators  (Hobson  1973). 
In  temperate  kelp  forests  near  Santa 
Barbara,  the  replacement  of  species  in  the 


Blue  Rockfish     <?)■& 



Kelp  Bass 


Blackeye  Goby 




Kelp  Rockfish 
Horizontal  scale  =  10  cm 

—     California  Sheephead 
Figure    22.       Some    common    kelp    forest    fishes    (redrawn    from    Miller  and  Lea  1972). 

water  column  at  dusk  is  not  as  dramatic; 
there  are  a  few  nocturnal  species,  but  the 
majority  are  diurnal  (Ebeling  and  Bray 
1976).  The  number  of  nocturnal  indivi- 
duals and  species,  however,  is  greater  in 
the  warmer  water  off  Catalina  Island 
(Hobson  and  Chess  1976,  Hobson  et  al . 
1981).  Species  that  are  of  tropical 
origin  do  show  the  apparently  programmed 
activity  pattern  of  tropical  species,  even 
though  predation  may  be  reduced  (Ebeling 
and  Bray  1976,  but  also  see  Hobson  et  al. 

Kelp  forest  fishes  can  be  divided 
into  two  groups  according  to  the  sub- 
habitat  occupied  within  kelp  forests: 
canopy-midwater  orienting  species,  and 
bottom-orienting  species.  Feeding 

categories  can  also  be  distinguished  for 
species  in  the  habitat  groups  (Table  9) 
and  include  browsers,  planktivores,  and 
predators  on  motile  prey  (Choat  1982). 
Browsers  feed  primarily  on  sessile  orga- 
nisms,   whereas    predators    on    mobile    prey 

(ambushers,  searchers,  chasers)  feed  on 
invertebrates  and  fishes.  Planktivores 
feed  on  open-water  zooplankton. 

4.5.2     Canopy-midwater  Species 

Only  two  species  can  truly  be 
classified  as  browsers  in  the  canopy-mid- 
water zones:  the  senorita  (Figure  22), 
Oxyjul ius  cal ifornica,  a  member  of  a 
tropical  family  (Labridae),  and  the  kelp 
surf perch  Brachyistius  frenatus  in  the 
temperate        family        Embiotocidae.  The 

senorita  is  an  orange-colored,  cigar- 
shaped  fish  with  a  pointed  snout  and 
protruding  teeth.  It  generally  swims  in 
schools  of  several  to  hundreds  of  indivi- 
duals, and  ranges  from  the  canopy  to  the 
bottom  (Bray  and  Ebeling  1974).  This 
species  is  a  daytime  feeder  on  the  bryo- 
zoan  Membranipora  sp.,  which  grows  on 
Macrocystis  pyrifera,  hydroids,  kelp- 
associated  crustaceans,  and  some  open- 
water  plankton  (Bernstein  and  Jung  1979). 
Bernstein   and   Jung    (1979)    suggested   that, 


Table  9.  Subhabitat  and  feeding  categories  of  common  kelp  forest  fishes. 




Predators  on 
mobile  prey 



Senori ta 
(Oxyjulis  californica) 

Kelp  surfperch 
(Brachyistius  frenatus) 

Ha  If moon  a 
(Medialuna  cal iforniensis ) 

(Hypsypops  rubicundus) 


California  sheephead 
(Semicossyphus  pulcher) 

Opal  eye a 
(Gi  rel  la  nigricans) 

Blue  rockfish 
(Sebastes  mystinus) 

(Chromis  punctipinnis) 

Juvenile  rockfish 
(Sebastes  spp. ) 

Juvenile  kelp  bass 
(Paralabrax  clathratus) 

Giant  kelpfish 
fHeterostichus  rostratus) 

Kelp  bass 
(Paralabrax  clathratus) 

Olive  rockfish 
(Sebastes  serranoides) 

Black  rockfish 
(Sebastes  melanops) 


California  Sheephead 
(Semicossyphus  pulcher) 

(Sebastes  spp. ) 

Greenl ing 
(Hexogrammos  spp.) 

(Ophiodon  elongatus) 

(Scorpaenichthys  marmoratus) 



Torpedo  ray 
(Torpedo  cal ifornica) 

eAlso  grazers. 

in  the  absence  of  senorita  predation,  kelp 
fronds  would  be  much  more  heavily  fouled 
by  sessile  animals,  and  perhaps  destroyed 
by  herbivorous  crustaceans.  Senoritas 
also  clean  other  fishes,  feeding  on  scales 
and  parasitic  copepods.  At  night,  this 
fish  buries  itself  in  patches  of  rubble 
and  sand,  a  characteristic  behavior  of 
many  labrids. 

The  diet  of  the  kelp  surfperch  is 
similar  to  that  of  the  senorita.  This 
kelp-colored  fish  consumes  copepods, 
gammarid  amphipods,  bryozoans,  and  occa- 
sionally ectoparasites  on  other  fish  (Bray 
and  Ebeling  1974,  Coyer  1979).  Kelp 
surfperch  feed  during  the  day,  usually 
starting  at  dawn,  and  have  full  stomachs 
by  noon.  This  species  is  very  rare  in 
areas  without  large  seaweeds  (Carr  pers. 
comm. ) . 

The  halfmoon  Medialuna  cal iforniensis 
(Family  Scorpididae,  Figure  22~)  iTs  a 
browser,  but  consumes  both  invertebrates 
and  algae  in  southern  California  (Quast 
1971d,  Feder  et  al.  1974).  The  halfmoon 
occurs  singly  or  in  loose  schools, 
browsing  on  seaweeds,  and  along  with  the 
opaleye  (see  below),  is  the  only  abundant, 
large  fish  that  regularly  feeds  on 
seaweeds  in  California  giant  kelp  forests. 
Other  than  an  occasional  bite  mark, 
halfmoon  appear  to  cause  little  damage  in 
large  stands  of  kelp.  If  stands  are 
reduced  to  a  few  plants,  however,  these 
fish  can  completely  remove  blades,  causing 
the  plants  to  die.  This  has  inhibited 
transplant  efforts  to  restore  giant  kelp 
(North  1968),  and  to  establish  Macrocystis 
and  Pterygophora  cal ifornica  on  a  large 
artificial  reef  (Grant  et  al.  1982,  LOSL 


Predators  feeding  on  large,  mobile 
prey  in  the  canopy-midwater  regions 
include  the  giant  kelpfish  (Heterostichus 
rostratus) ,  the  kelp  bass  (Paralabrax 
clathratus) ,  the  kelp  rockfish  (Sebastes 
the  olive  rockffsh  (S. 
and  the  black  rockfish  (_S. 
Young  olive   rockfish   eat 

atrovirens) , 


melanops) . 

plankton  (Hobson  and  Chess  1976,  Love  and 

Ebeling  1978). 

The  cryptically-colored  giant 
kelpfish  occurs  throughout  the 
water-column  in  close  association  with 
Macrocystis  and  other  seaweeds.  Although 
rarely  seen  in  central  California,  it  is 
particularly  common  in  kelp  forests  around 
islands  off  southern  California.  The 
giant  kelpfish  feeds  during  the  day  in 
open  water,  on  substratum-oriented  prey 
such  as  mysids,  isopods,  amphipods,  shrimp 
and  fish  (Coyer  1979,  Hobson  et  al .  1981). 

The  kelp  bass  (Figure  22)  was 
described  by  Quast  (1968,  1971a)  as  a 
medium-sized,  generalized  carnivore 
occupying  a  wide  variety  of  environments. 
Kelp  bass  tend  to  move  only  slightly  among 
reefs  (Young  1963)  and  will  congregate  at 
heavily  fished  and  chummed  sites.  Food 
habits  change  with  age;  juveniles  (<  299 
mm)  eat  primarily  benthic  invertebrates 
and  plankton,  but  switch  to  fish  when  they 
grow  larger  (Love  and  Ebeling  1978,  Hobson 
et  al.  1981).  Kelp  bass  over  30  cm  eat 
predominately  fish,  although  invertebrates 
occasionally  are  found  in  their  stomachs. 
In  southern  California,  kelp  bass  are 
regarded  as  one  of  the  primary  fish 
predators  in  the  kelp  forest.  This 
species  is  not  as  common  in  central 
Cal ifornia. 

The  kelp  rockfish  (Figure  22),  a 
common  cryptic  species,  can  be  found 
throughout  the  water  column  associated 
with  kelp.  Kelp  rockfish  hover  adjacent 
to  kelp  stipes,  during  the  day  and  night 
in  central  California,  but  both  rest  on 
the  bottom  and  hover  at  night  in  southern 
California  (Hobson  and  Chess  1976,  Van 
Dykhuizen  1983).  They  feed  on  a  wide  size 
range  of  prey  items,  including  plankton, 
epibenthic  invertebrates,  and  juvenile 
fishes.  Kelp  rockfish  feed  primarily  at 
dawn  and  at  night,  but  will  take  prey 
whenever  it  is  abundant. 

The  olive  rockfish  (Figure  22), 
common  to  both  central  and  southern 
California  kelp  forests,  is  a  large 
midwater  predator.  Unlike  kelp  bass, 
which  they  superficially  resemble,  adult 
olive  rockfish  generally  remain  in  the 
same  location  on  a  particular  reef  (Love 
1980).  Juveniles,  subadults,  and  adults 
differ  in  their  feeding  behavior  (Hobson 
and  Chess  1976,  Love  and  Ebeling  1978, 
Love  and  Westphal  1981).  Juvenile  olive 
rockfish  <  55  mm  form  aggregations  in  the 
water  column,  and  feed  on  copepods, 
amphipods  and  larvae.  Intermediate-sized 
juveniles,  55-65  mm,  feed  day  and  night  on 
amphipods,  cumaceans,  and  mysids.  Large 
juveniles  (>  65  mm)  are  active  at  night, 
hovering  in  midwater  aggregations  over  the 
bottom,  and  feeding  on  amphipods,  mysids, 
and  other  crustaceans.  Adults  may  feed 
day  or  night  on  juvenile  fishes,  octopus, 
and  squid.  The  local  distribution  and 
food  habits  of  the  olive  rockfish  in 
central  California  are  similar  to  those  of 
the  kelp  bass  in  southern  California  (see 
discussion  in  Love  and  Westphal  1981). 

Black  rockfish  are  rare  in  southern 
California  kelp  forests,  but  common  in 
central  California.  This  species  occupies 
the  midwater  zone,  solitary  or 
interspersed  with  schools  of  blue 
rockfish.  Juvenile  rockfish  are  important 
prey  for  the  black  rockfish  during  the 
upwelling  period  (spring-early  summer), 
while  polychaetes  are  important  prey  at 
other  times  of  the  year  (Roberts  1979). 

Kelp  forest  fishes  that  feed 
predominantly  on  plankton  include  blue 
rockfish  (Sebastes  mystinus) ,  the 
blacksmith  (Chromis  punctipinnus) ,  and 
juvenile  rockfishes  (Sebastes  spp. ) .  Blue 
rockfish  (Figure  22)  are  the  most  common 
rockfish  in  the  kelp  forests  of  central 
and  southern  California.  They  occupy  the 
open-water  habitat  in  kelp  forests  or  over 
deep,  rocky  reefs  devoid  of  kelp. 
Individuals  of  this  species  occur  alone, 
in  loose  schools,  or  in  large  aggregations 
(Miller  and  Geibel  1973).  Blue  rockfish 
are  also  one  of  the  most  important  sport 
species  in  central  and  northern  California 
(Miller  and  Geibel  1973).  The  habitats  of 
the  blue  rockfish  in  central  California 
are  similar  to  those  of  the  blacksmith 
(see  below)  in  southern  California.  The 
feeding  habits  of  the  blue  rockfish  differ 


between  the  upwelling  and  non-upwel 1 ing 
seasons  (Miller  and  Geibel  1973,  Love  and 
Ebeling  1978,  Roberts  1979).  Pelagic 
tunicates  and  crustaceans  are  important 
prey  in  the  upwelling  season,  whereas 
algae,  euphausids  and  larval  fishes  are 
eaten  in  the  non-upwelling  season. 
Hallacher  (1977)  also  found  algae  in  blue 
rockfish  stomachs. 

The  most  common  fish  in  the  kelp 
forests  of  southern  California  is  the 
blacksmith  (Figure  22).  This  damselfish 
usually  aggregates  in  the  midwater  on  the 
up-current  edge  of  kelp  forests  during  the 
day.  It  feeds  on  larvaceans,  copepods, 
cladocerans,  and  various  larvae. 
Blacksmith  retreat  to  shelter  holes  and 
crevices  at  dusk  and  come  out  again  at 
dawn  (Bray  1981).  As  a  result  of  feeding 
on  plankton  at  the  edge  of  kelp  forests 
during  the  day  and  defecating  in  the 
shelter  holes  at  night,  blacksmith 
transport  extrinsic  energy  into  the  kelp 
forest,  and  their  feces  provide  a  food 
source  for  the  benthic  invertebrates  (Bray 
et  al.  1981). 

Juvenile  rockfishes  are  the  most 
abundant  planktonic  feeders  during  the 
upwelling  season  in  central  California 
(Burge  and  Schultz  1973).  They  recruit  to 
kelp  forests  initially  around  May,  and 
remain  there  until  November  or  December 
when  winter  storms  begin.  The  seven 
species  studied  by  Singer  (1982)  were 
divided  into  two  groups:  those  which  fed 
primarily  in  the  water  column,  and  those 
which  fed  on  substrate-oriented  prey.  All 
species  were  generally  active  and  fed 
during  the  day.  These  juvenile  rockfishes 
provide  an  important  source  of  prey  for 
many  adult  kelp  forest  fishes,  including 
kelp  bass  (Young  1963),  adult  rockfishes 
(Roberts  1979,  Love  and  Westphal  1981), 
and  ling  cod  (Miller  and  Giebel  1973). 
Many  nearshore  birds  also  feed  on 
young-of-the-year  rockfish  in  kelp  forests 
(Follett  and  Ainley  1976,  Hubbs  et  al. 
1970,  Ainley  et  al.  1981,  Carr  1983). 

A  number  of  small  cryptic  fishes 
occupy  the  surface  and  midwater  portions 
of  the  water  column,  but  only  in  the 
presence  of  Macrocystis  pyrifera.  The 
kelp  gunnel  (Ulvicola  sanctaerosae) ,  kelp 
clingfish  (Rimicola  muscarum) ,  giant 
kelpfish  (Heterostichus  rostratus)  and  the 

manacled  sculpin  (Synchirus  gil 1 i )  all 

maintain   close  proximity   to   vertical 

fronds  and  the  canopy  of  giant  kelp, 

feeding  on  small,  mobile  prey. 

As  pointed  out  in  the  introduction, 
almost  all  fishes  found  in  kelp  forests 
can  be  found  in  rocky  habitats  without 
kelp.  The  relative  importance  of  the 
Macrocystis  habitat,  however,  may  be  much 
greater  for  the  early  life  stages  of  some 
fishes  than  for  adult  conspecifics. 
During  this  early  period  of  high 
vulnerability  to  predation  and  pressing 
metabolic  requirements  for  growth,  the 
refuge  made  available  by,  and  prey  species 
associated  with,  kelp  structure  may 
enhance  local  survivorship  of  recently 
recruited  fishes.  The  abundance  of  young 
rockfish  (Leaman  1976,  Burge  and  Schultz 
1973,  Miller  and  Giebel  1973,  Carr  1983) 
and  kelp  bass  (Larson  and  DeMartini  in 
press)  throughout  the  water  column  in  kelp 
seems  to  be  strongly  influenced  by  the 
presence  of  M.  pyrifera. 

4.5.3  Bottom  Species 

Fishes  that  occur  in  the  bottom  zone 
of  kelp  forests  can  also  be  classified  as 
browsers  or  predators  on  mobile  prey. 
Here  again,  there  are  differences  with 
respect  to  species  composition  between 
central  and  southern  California.  Browser- 
type  fishes  feeding  on  sessile 
invertebrates  include  the  garibaldi 
(Hypsypops  rubicunda) ,  the  rock  wrasse 
(Halichoeres  semicinctus) ,  and  some  of  the 
surfperches  (Embiotocidae). 

The  most  visible  fish  in  the  bottom 
zone  is  the  bright  orange  ocean  goldfish 
or  garibaldi  (Figure  22).  It  ranges  north 
to  Monterey  Bay,  but  is  rare  north  of 
Point  Conception  (Miller  and  Lea  1972). 
Garibaldi  defend  territories  which  include 
a  feeding  area,  a  shelter  hole,  and  for 
some,  a  breeding  site  (Clarke  1970,  1971). 
Territories  are  defended  throughout  the 
year,  and  up  to  four  years  at  the  same 
site.  Some  garibaldi  are  not  territorial; 
juveniles  do  not  defend  territories,  and 
females  do  not  defend  home  ranges  as 
strictly  as  males.  The  nesting  site 
consists  of  a  patch  of  filamentous  algae 
that  is  kept  free  of  other  organisms  and 
detritus  by  the  male  during  the  breeding 
season.   This  tends  to  increase  algal 


branch  density,  which  then  decreases  after 
the  breeding  season  (Foster  1972).  Female 
garibaldi  lay  eggs  on  this  turf  from  May 
to  October,  and  young  disperse  in  the 
plankton  and  settle  in  shallow  water 
(Clarke  1970).  Newly  settled  garibaldi 
feed  on  copepods,  isopods,  cladocerans, 
and  amphipods.  Adults  feed  on  sponges, 
cnidarians,  bryozoans  and  sometimes, 
polychaetes,  nudibranchs,  and  crabs.  This 
species  is  active  by  day,  retreating  to 
shelter  holes  at  night. 

Surfperches  in  the  Family 
Embiotocidae  are  extremely  common  in 
temperate  fish  assemblages.  Members  of 
this  family  are  viviparous,  giving  birth 
to  live  young  which  already  resemble  the 
adults.  The  surfperches  feed  primarily  on 
small  crustaceans,  brittle  stars,  clams, 
mussels,  limpets,  polychaetes,  and  snails 
which  inhabit  the  "turf"  on  the  rocky 
substrate  (Feder  et  al.  1974,  Ellison  et 
al.  1979,  Haldorson  and  Moser  1979,  Laur 
and  Ebeling  1983).  The  most  common 
surfperches  observed  in  southern 
California  kelp  forests  are  the  black 
surfperch  (Embiotoca  jacksoni,  Figure  22), 
white  surfperch  (Phanerodon  furcatus) ,  and 
the  pile  perch  (Damal ichthys  vacca). 
Rainbow  perch  (Hypsurus  caryi ) ,  and 
rubberlip  surfperch  (Rhacochilus  toxotes) 
are  also  commonly  observed  near  the 
bottom,  feeding  in  turf.  The  striped 
surfperch  (_E.  lateralis)  occurs  off  Santa 
Barbara  but  is  much  more  abundant  off 
California  (Haldorson  and  Moser 
Many  surfperches  are  able  to 
the  turf  material  ,  select  and 
the  preferred  food  items,  and 





reject  the  undesired  material 

The  sheephead  (Semicossyphus  pulcher, 
Figure  22),  a  member  of  the  wrasse  family, 
is  a  common  reef  inhabitant  in  southern 
California.  This  species  is  a  protogynous 
hemaphrodite  (females  change  into  males), 
with  the  female  coloration  being  uniformly 
red  or  purple  with  a  white  chin,  and  the 
males  having  a  black  body  with  a  pink  band 
behind  the  head  and  a  white  chin. 
Sheephead  are  solitary  wanderers,  feeding 
(by  crushing  food  in  the  throat  before 
swallowing)  on  urchins,  mussels,  crabs, 
snails,  squid,  and  bryozoans  (Feder  et  al. 
1974).  Tegner  and  Dayton  (1981)  suggested 
that  sheephead  may  have  a  significant 
effect  on  sea  urchin  abundance,  and  Nelson 

and  Vance  (1979)  suggest  that  the  behavior 
of  the  sea  urchin  Centrostephanus 
coronatus  is  related  to  sheephead 
predation.  Cowen  (1983),  working  on  a 
reef  at  San  Nicolas  Island,  found  that 
Strongyl ocentrotus  franciscanus  densities 
increased,  and  distribution  changed  when 
sheephead  were  removed.  Sheephead  do  not 
appear  to  be  important  predators  on  sea 
urchins  in  the  mainland  kelp  forest  at  San 
Onofre  (Dean  et  al .  1984).  Sheephead 
retreat  to  shelter  holes  at  night,  and 
some  produce  a  mucous  envelope  that 
surrounds  the  body  (Wiley  1973). 

Like  the  midwater  canopy-dwelling 
half moon,  the  opal  eye  Girella  nigricans 
(Family  Girellidae,  Figure  22)  browses  on 
both  invertebrates  and  algae  (Quast  1971d, 
Feder  et  al .  1974),  and  can  cause 
extensive  damage  to  isolated  giant  kelp 
plants  (see  discussion  under  halfmoon 
above).  Opaleye  are  extremely  common  in 
southern  California  kelp  forests,  but 
relatively  rare  north  of  Point  Conception. 

The  rockfishes  (Scorpaenidae)  are  an 
important  constituent  of  the  bottom- 
dwelling  fauna  of  kelp  forests  in  central 
California  (Hallacher  1977).  The  common 
demersal  species  are  the  grass  rockfish 
(Sebastes  rastrell iger) ,  black-  and-yellow 
rockfish  (S.  chrysomelas) ,  gopher  rockfish 
[S.  carnatus) ,  copper  rockfish  (S. 
caurinus) ,  aTTd  treefish  (S.  serricepsj. 
The  grass  rockfish  is  generally  restricted 
to  rocky  bottoms  <  30  m  deep  where  it  eats 
crabs  and  small  fishes  (Feder  et  al. 
1974).  Copper  rockfish,  although  not 
abundant,  inhabit  rocky  reef  areas  with  or 
without  kelp.  This  species  feeds 
primarily  on  crabs,  shrimp,  cephalopods, 
and  fishes  (Feder  et  al.  1974,  Prince 
1975).  The  black-and-yel  low  and  gopher 
rockfishes  are  territorial  and  are 
segregated  by  depth  (Larson  1980a,  b,  c). 
These  two  species  feed  on  similar  prey 
such  as  crabs,  shrimp  and  octopus. 
Treefish  are  common  in  southern 
California,  but  rare  in  central  California 
(Miller  and  Lea  1972).  Treefish  are 
territorial,  inhabiting  rocky  crevices 
(Feder  et  al .  1974).  They  feed  on  shrimp, 
crabs,  and  fishes  at  nocturnal  or 
crepuscular  hours  (Hobson  et  al.  1981). 

Fishes  belonging  to  the  greenling 
family  (Hexagrammidae)  are  also  commonly 


observed  in  the  bottom  zone.  These 
species  include  the  painted  greenling 
(Oxylebius  pictus),  kelp  greenling 
(Hexagrammos  decagrammus) ,  and  the  lingcod 
(Ophiodon  elongatus).  Hexagrammidae  eggs 
are  attached  to  rocks  and  are  often 
guarded  by  the  male.  The  painted  green- 
ling feeds  on  small  epibenthic  crustace- 
ans. Adult  males  are  brightly  colored  and 
aggressive  during  the  breeding  season 
(DeMartini  and  Anderson  1980).  They 
defend  both  a  spawning  site  and  a  shelter 
hole,  while  females  defend  shelter  holes 
only.  The  kelp  greenling  is  also  sexually 
dimorphic.  This  species  feeds  primarily 
on  polychaetes,  crustaceans,  and  small 
fishes  (Feder  et  al.  1974).  The  kelp 
greenling  is  rare  in  southern  California, 
and  occurs  in  waters  deeper  than  20  m. 
The  lingcod  (Figure  22),  a  prized  sport 
fish,  is  a  seasonal  migrant  to  kelp 
forests.  Lingcod  enter  shallow  waters  to 
lay  and  guard  eggs.  Males  guard  nests  for 
about  seven  weeks,  and  often  guard  two  to 
four  nests  simultaneously.  Their  diet 
consists  of  crabs,  cephalopods,  and  fishes 
(Miller  and  Geibel  1973).  Some  lingcod 
remain  as  residents  of  kelp  forests,  while 
others  migrate  to  deeper  waters. 

Sculpins  in  the  Family  Cottidae  are 
cryptic  bottom  fishes  that  can  be  very 
abundant,  and  difficult  to  see.  A  large 
member  of  this  family,  the  cabezon, 
(Scorpaenichthys  marmoratus)  is  often  seen 
resting  on  the  bottom  and  is  easily 
approached.  Cabezon  are  often  caught  by 
fishermen.  The  eggs  are  poisonous  to 
humans  and  should  not  be  eaten.  This 
species  feeds  on  crustaceans  and  molluscs, 
including  abalone  (O'Connell  1953,  Feder 
et  al.  1974).  Other  common  subtidal 
sculpins  include  the  lavender  (Leiocottus 
hirundo)  and  the  snubnose  (Orthonopias 
triacis) .  They  feed  primarily  on 
epibenthic  crustaceans. 

Gobies  in  the  Family  Gobiidae  are 
small  demersal  fishes,  often  observed 
while  scuba  diving.  The  blackeyed  goby 
(Coryphopterus  nicholsi  i ,  Figure  22)  is 
usually  observed  in  sandy  areas  near 
rocks.  Nesting  occurs  from  April  to 
October,  with  the  male  first  cleaning  a 
spawning  site  under  a  rock.  The  female 
lays  eggs,  and  the  male  guards  the  nest 
(Wiley  1973,  Feder  et  al.  1974).  The 
blue-banded  goby  (Lythrypnus  da  1 1 i )  is  a 

strikingly  colorful  fish  common  only  in 
southern  California.  This  species  is 
brilliant  crimson  or  orange-red  with  about 
six  iridescent,  blue,  vertical  stripes  on 
the  anterior  two  thirds  of  the  body. 
Blue-banded  gobies  are  omnivorous,  but 
feed  primarily  on  demersal  zooplankton, 
especially  amphipods  (Feder  et  al.  1974). 
The  zebra  goby  (Lythrypnus  zebra)  is  a 
more  cryptic  species  with  similar 

Within  habitats,  fish  species  may 
segregate  by  food  supply.  Hixon  (1980) 
and  Larson  (1980a)  provided  the  first 
experimental  evidence  that  closely  related 
species  that  occur  in  the  bottom  zone  may 
partition  space  along  a  depth  gradient  in 
food  availability.  In  each  of  two  pairs 
of  congeners,  a  competitively  dominant 
microhabitat  specialist  excluded  a 
subordinate  general  1st  from  the  shallow 
zone  where  prey  was  more  abundant. 
Predictably,  the  general ist  expanded  its 
distribution  into  shallow  water  when  the 
specialist  fish  was  removed  by  spearing. 
The  specialist  fish  remained  in  shallow 
water  in  the  absence  of  the  general ist. 
Thus,  bathymetric  partitioning  was 
maintained  by  interference  competition. 

4.5.4  Other  Species 

An  important  predatory  fish,  the 
torpedo  ray,  (Torpedo  cal ifornica;  Figure 
22),  is  most  commonly  observed  in  southern 
California.  This  species  generally  enters 
the  kelp  forest  at  night  to  feed  on 
fishes,  usually  by  initially  shocking  its 
prey,  and  then  eating  it  whole  (Bray  and 
Hixon  1978).  The  torpedo  ray  hovers 
motionless  above  the  bottom,  apparently 
waiting  for  fishes  to  approach  within  its 
shocking  range. 

Sharks  and  rays,  which  are 
occasionally  observed  in  kelp  forests, 
include  the  bat  ray  (Myl iobatis 
cal ifornica) ,  the  horn  shark  (Heterodontus 
franc isci ) ,  the  leopard  shaTk  (Triakis 
semifasciata) ,  the  angel  shark  (Squatina 
cal  ifornica)  and  the  swell  shark 
(Cephaloscyll  ium  ventriosum) .  Bat  rays 
are  usually  found  buried  in  sand  or 
resting  on  rocks.  They  feed  on  shellfish 
such  as  abalone  and  turban  and  top  snails 
(Feder  et  al.  1974),  and  may  be  seen 
grubbing  for  other  prey  in  sand  channels 


between  rocky  reefs  (Cowen  pers.  comm.). 
Horn  sharks  are  frequently  found  in 
crevices  or  among  rocks.  They  feed  at 
night  on  large  crustaceans  and  small 
fishes.  The  spiral-shaped  egg  cases  are 
often  scattered  among  rocks  (Feder  et  al . 
1974).  Leopard  sharks  enter  kelp  forests 
for  short  periods,  usually  resting  on  the 
bottom.  They  eat  crustaceans  and  small 
fishes.  The  angel  shark  buries  in  sand  or 
mud,  where  it  ambushes  fishes  such  as 
corbina  and  queenfish  (Feder  et  al .  1974). 

Other  occasional  visitors  to  kelp 
forests  include  barracuda  (Sphyraena 
argentea) ,  Pacific  bonito  (Sarda 
chilensis) ,  ocean  sunfish  or  common  mola 
(Mola  mola) ,  giant  sea  bass  (Stereolepis 
gigas) ,  the  salema  (Xenistius 
cal iforniensis) ,  and  the  jack  mackerel 
(TrachuruT  symmetricus).  Schools  of 
barracuda  and  Pacific  bonito  enter  kelp 
forests  while  pursuing  anchovies  or 
sardines  (Feder  et  al .  1974).  Ocean 
sunfish  are  weak-swimming  pelagic  fish 
that  are  swept  into  kelp  forests  via 
currents.  Senoritas  and  kelp  surfperch 
remove  ecotoparasites  from  ocean  sunfish. 
Common  molas  lack  teeth,  and  consume 
soft-bodied  prey  such  as  jellyfish  and 
salps.  The  giant  sea  bass  was  once  common 
in  southern  California,  but  its  numbers 
have  been  severely  decreased  by 
overfishing.  Individuals  swim  2-3  m  above 
the  substrate,  and  feed  on  spiny  lobsters, 
squid,  and  fishes  (Feder  et  al.  1974). 
Salema  and  jack  mackerel  may  form  large 
schools  in  kelp  forests  during  summer  and 
early  fall  when  the  water  is  warmer. 


4.6.1  Birds  Introduction.  The  associa- 
tion of  birds  with  California  kelp  forests 
is  poorly  known,  and  is  limited  to 
generalized  accounts.  Due  to  the  paucity 
of  published  literature,  much  of  the 
discussion  below  will  be  based  on  personal 

North  (1971b)  does  not  include  any 
birds  in  his  list  of  the  kelp  bed  fauna 
for  southern  California  and  northern  Baja 
California,  Mexico.  However,  he  does 
mention  birds  as  being  top  carnivores  in 
the  kelp  community.   Davis  and  Baldridge 

(1980)  acknowledged  that  seabirds  often 
frequent  kelp  forests.  Angell  and  Balcomb 
(1982)  reported  that  the  edges  of  Puget 
Sound,  Washington  kelp  beds  are 
"patrolled"  by  guillemots,  auklets,  and 
pelagic  cormorants.  Page  et  al .  (1977) 
characterized  the  inshore  bird  assemblage 
as  being  made  up  of  loons,  grebes, 
cormorants,  scoters,  and  pigeon 
guillemots.  The  only  quantitative  study 
of  bird-kelp  forest  association  is  Hubbs 
et  al.  (1970),  who  documented  the  diet  of 
Brandt's  cormorants. 

Kelp  provides  three  distinct  habitats 
used  by  birds: 

1.  Kelp  Forest:  Living,  attached 
kelp  in  association  with  rocky  substrata. 

2.  Drift  Kelp:  Detached  kelp  that 
may  be  found  floating  far  out  to  sea  in 
the  pelagic  zone. 

3.  Kelp  Wrack:  Detached  kelp 
deposited  on  the  beach  by  water  motion. 

The  discussion  below  is  organized  by 
these  habitats.  Ashmole  (1971)  should  be 
consulted  for  details  of  the  feeding 
methods  of  the  seabirds  described.  Kel p  forests.  Kelp  forests, 
with  their  associated  invertebrates  and 
fishes,  provide  a  large  potential  food 
supply  for  birds.  In  addition,  a  well- 
developed  kelp  canopy  reduces  water 
motion,  serving  as  a  refuge  from  storms. 
From  the  standpoint  of  bird  use,  kelp 
forests  can  be  conveniently  divided  into 
three  somewhat  distinct  subhabitats:  (1) 
the  surface  canopy;  (2)  the  midwater  and 
the  bottom  substrata  beneath  the  canopy; 
and  (3)  the  seaward  fringe  of  the  forest. 
The  common  birds  in  each  subhabitat  are 
listed  in  Table  10,  and  are  discussed 

Surface  canopy.  A  well-developed 
canopy  forms  a  buoyant  mat  on  which  birds 
may  perch.  The  degree  of  canopy 
development  is  probably  the  most  important 
factor  in  determining  the  numbers  and 
diversity  of  birds  that  will  be  present. 
Seasonal  variations  in  canopy  development 
dictate  the  degree  to  which  kelp  forests 
will  be  utilized  by  birds. 

Baldridge  (pers.  comm.)  observed 
large  numbers  of  elegant  terns  (Sterna 
elegans,  Figure  23)  and  Heermann's  gulls 


Table  10.  Birds  of  kelp  forests  and  their  subhabitat  use. 

Surface  canopy 

Midwater  and  bottom 

Seaward  fringe 

Elegant  tern 
(Thalasseus  elegans) 

Heermann's  gull 
(Larus  heermanni ) 

Western  gull 
(Larus  occidentalis) 

Bonaparte's  gull 
(Larus  Philadelphia) 

Great  blue  heron 
(Ardea  herodias) 

Snowy  egret 
(Leucophoyx  thula) 


Wandering  tattler 
(Heteroscelus  incanum) 

Northern  phalarope 
(Lobipes  lobatus) 

Pelagic  cormorant 
(Phalacrocorax  pelagicus) 

Brandt's  cormorant 
(Phalacrocorax  penicil latus) 

Horned  grebe 
(Podiceps  auritus) 

Eared  grebe 
(Podiceps  caspicus) 

Brown  pelican 
(Pelecanus  occidental  is) 

Common  loon 
(Gavia  immer) 

Western  grebe 
(Aechmophorus  occidentalis) 

Brandt's  cormorant 
(Phalacrocorax  penicil latus) 

Pelagic  cormorant 
(Phalacrocorax  pelagicus) 

Surf  scoter 
(Melanitta  perspicul lata) 

White-winged  scoter 
(Melanitta  deglandi ) 

Pigeon  guillemot 
(Cepphus  columba) 

Common  murre 
(Uria  aalge) 

(Larus  heermanni )  roosting  on  the  kelp 
forest  off  Pacific  Grove,  California. 
Elegant  terns  inhabit  California  waters 
from  July  to  November  (Page  et  al.  1977). 
They  pick  small  fishes  from  the  canopy  by 
surface  plunging  (Angel  1  and  Balcomb 

Heermann's  gulls,  western  gulls 
(Larus  occidentalis,  Figure  23),  and 
Bonaparte's  gulls  (J_.  Philadelphia) 
scavenge  on  the  surface  kelp  canopy.  On 
San  Nicolas  Island  in  southern  California, 
western  gulls  pick  the  large  grazing 
gastropod  Norrisia  norrisi  from  giant  kelp 
canopies,  and  drop  the  snails  on  rocky 
ledges  on  shore.  The  impact  breaks  the 
thick  shell  so  the  gulls  can  then  feed  on 
the  meat  (Reed  pers.  comm.).  Western 
gulls  are  year-round  residents  of 
California.   Bonaparte's  gull  overwinters 

in  California,  and  Heermann 
found  in  the  summer  and  fall 
et  al.  1977). 

s  gull  can  be 
seasons  (Page 

great   blue   heron   (Ardea 

and  the  snowy  egret  (Egretta 

winter  along  coastal  California, 


and  can  often  be  seen  perched  on  the  kelp 
canopy,  frozen  in  motion,  silently 
stalking  prey  at  the  water's  surface 
(Figure  23).  Occasional  shorebirds  such 
as  the  wandering  tattler  (Heteroscelus 
incanus) ,  and  the  willet  (Catoptrophorus 
semipalmatus)  may  forage  on  the  surface  of 
kelp  forests  (Baldridge  pers.  comm.). 
Jameson  (pers.  comm.)  suggests  that  the 
heron  feeds  on  juvenile  rockfish  and  other 
small  fishes  in  the  canopy,  egrets  feed  on 
isopods  and  kelp  crabs,  and  willets  on 
isopods.  His  observations  also  suggest 
that  some  of  these  birds  may  establish 


Common  Loon 

Common  Murre 
Horizontal  scale  =  20  cm 

Elegant  Tern 
Figure  23.   Birds  commonly  associated  with  kelp  forests. 

regular  feeding  territories  in  the  canopy, 
particularly  if  freshwater  feeding  areas 
are  limited. 

While  diving  in  kelp  forests,  Foster 
(pers.  obs.)  observed  the  northern 
phalarope  (Lobipes  lobatus)  feeding  on 
plankton  within  openings  in  the  canopy. 
The  common  loon  (Gavia  immer,  Figure  23), 
western  grebe  (Aechmorphorus  occidental  is, 
Figure  23),  surf  scoter  (Melanitta 
perspicillata,  Figure  23),  and  white- 

winged  scoter  (M.  deglandi )  may  also  use 
California  kelp  forests  with  large  open 
areas  within  the  canopy  (Baldridge  pers. 
comm. ). 

Midwater  and  bottom. 


all   the 


birds,  the  Brandt's 
(Phalacrocorax  pennicillatus,  Figure  23), 
and  possibly  the  pelagic  cormorant  (P. 
pelagicus,  Figure  23)  are  most  closely 
associated  with  California  kelp  forests 
(Ainley  pers.  comm.).  Hubbs  et  al .  (1970) 


described  Brandt's  cormorants  in  the 
vicinity  of  San  Diego,  California,  as 
occupying  a  variety  of  habitats,  but 
especially  the  large  Macrocystis  forest 
off  La  Jolla.  Cormorants  feed  by  foot- 
propelled  pursuit  diving  but  may  also  use 
their  wings  underwater  (Cowen  pers. 
comm.).  The  stomach  contents  of  eight 
Brandt's  cormorants  from  San  Diego  kelp 
forests  revealed  that  they  fed  almost 
exclusively  on  fishes  that  inhabit  the 
midwater  among  the  fronds  of  Macrocystis 
(Hubbs  et  al.  1970).  These  included  the 
senorita  (Oxyjul is  cal ifornica) ,  the 
blacksmith  (Chromis  punctipinnis) ,  and  the 
kelp  perch  (Brachyistius  f ranatus)  (see 
Section  4.5).  The  pelagic  cormorant  has 
similar  feeding  habits  (Ainley  et  al. 
1981).  Both  cormorants  are  year-round 
residents  of  California. 

Ainley  and  Sanger  (1979)  included 
mysid  shrimp  as  a  major  prey  item  of  the 
horned  grebe  (Podiceps  guritus) ,  and  the 
eared  grebe  (_P.  niaricul  lis,  Figure  23), 
two  species  that  winter  along  the 
California  coast.  These  small  birds  are 
foot-propelled  pursuit  divers,  and  are 
commonly  observed  within  kelp  forests 
(Baldridge  pers.  comm.).  It  is  probable 
that  they  exploit  the  dense  swarms  of 
mysids  found  within  the  midwaters  of  the 
kelp  community  (see  Section  4.2). 

Seaward  fringe.  The  fringe  areas  of 
kelp  forests  probably  support  the  greatest 
diversity  of  birds.  The  interface  between 
kelp  and  open  waters  often  contains  dense 
aggregations  of  invertebrates  and  fishes, 
perhaps  because  currents  are  reduced  (see 
Section  2.2).  The  brown  pelican 
(Pelicanus  occidental  is  cal ifornicus, 
Figure  23)  along  with  terns  (Family 
Laridae)  are  surface-plunging  species  that 
may  exploit  concentrations  of  schooling 
fishes  along  the  canopy's  edge.  The  loons 
(Family  Gaviidae),  grebes  (Family 
Podicipedidae) ,  cormorants  (Family 
Phalacrocoracidae) ,  and  scoters  (Family 
Anatidae)  are  all  foot-propelled  pursuit 
divers  that  may  opportunistically  forage 
along  the  edges  of  kelp  forests. 

Pigeon  guillemots  (Cepphus  columba, 
Figure  23)  forage  by  wing-propelled 
pursuit,  diving  nearshore  during  spring, 
summer,  and  fall  (Page  et  al.  1977). 
Angel  1  and  Balcomb  (1982)  reported  that 

pigeon  guillemots  dive  for  prey  along  the 
edges  of  kelp  beds  within  the  Puget  Sound, 
Washington  area.  Follett  and  Ainley 
(1976)  studied  the  diet  of  pigeon 
guillemots  on  Southeast  Farallon  Island, 
and  found  that  they  had  fed  upon  24 
species  of  fish,  the  majority  of  which 
were  benthic.  Common  murres  (Uria  aalge, 
Figure  23)  also  forage  via  wing-propelled 
pursuit  diving,  concentrating  on  open- 
water  fish  species  and  squid  (Croll  pers. 
comm.).  They  may  also  feed  on  the  edges 
of  kelp  forests. 

The  majority  of  subsurface  diving 
seabirds  do  not  occur  in  the  kelp  canopy, 
but  may  be  abundant  at  the  canopy's 
fringe.  With  increased  kelp  density, 
subsurface  diving  may  be  restricted  due  to 
the  possibility  of  entanglement  of  feet  or 
wings  (depending  on  the  birds'  mode  of 
underwater  locomotion).  Drift  kelp.  Plankton  and 
small  fishes  often  concentrate  around 
drift  kelp  in  pelagic  waters.  The  red 
phalarope  (Phalaropus  ful icarius)  and  the 
northern  phalarope  ( Lob i pes  lobatus)  are 
found  in  California  waters  in  summer  and 
fall,  and  often  feed  in  association  with 
drift  kelp  far  out  to  sea.  Phalaropes  are 
believed  to  feed  by  seizing  planktonic 
organisms  at  the  water's  surface  (Page  et 
al .  1977).  Seabirds  may  also  use  pelagic 
draft  kelp  as  a  roosting  site  (Keating 
pers.  comm.).  Kelp  wrack.  Although  some 
drift  seaweed  is  usually  found  covering 
the  intertidal  zone  in  the  vicinity  of 
rocky  areas,  the  export  of  large  amounts 
of  kelp  to  beach  areas  is  a  seasonal  event 
associated  with  intense  wave  action  from 
fall  and  winter  storms.  Beach  drift  can 
support  a  microcosm  of  invertebrates  (kelp 
flies,  fly  maggots,  beetles,  various 
crustaceans,  etc.)  that  are,  in  turn, 
available  to  birds  as  prey  items  (Yaninek 
1980).  A  diversity  of  shore  and 
terrestrial  birds  forage  upon  algal  wrack 
on  a  seasonal  basis  (Davis  and  Baldridge 
1980).  Sanderlings  (Cal i dri s  alba) ,  black 
turnstones  (Arenaria  melanocephala) ,  and 
ruddy  turnstones  (A.  interpres),"  three 
opportunistically  feeding  shorebirds, 
regularly  pick  through  kelp  wrack.  Common 
crows  (Corvus  brachyrhynchos) ,  starlings 
(Sturnus    vulgaris) ,    and    brewer's 


blackbirds  (Auphaqus  cyanocephalus)  dig 
through  beach-cast  wrack  in  search  of 
marine  invertebrates  and  insects,  and  the 
latter  also  catch  beach  flies.  Beds  of 
decomposing  kelp  along  central  and 
southern  California  beaches  attract  black 
phoebes  (Sayarnis  nigricans) ,  house 
sparrows  (Passer"  demesticus) ,  and 
yellow-rumped  warblers  ("Dendrioca 
coronata)  that  feed  on  flies  and  other 
insects  (Davis  and  Baldridge  1980). 

Jameson  (pers.  comm.  )  also  observed  a 
variety  of  birds  feeding  on 
drift-associated  invertebrates,  and  in  the 
case  of  physically  unstable  cobble 
beaches,  he  pointed  out  that  this  drift 
can  change  an  otherwise  food-poor  habitat 
into  a  rich  feeding  area  for  birds.  He 
noted  intense  nearshore  feeding  by  gulls 
around  partially  decomposed  drift  when  the 
drift  is  moved  back  into  the  water  during 
high  tides  or  storms,  and  suggests  that 
the  gulls  may  be  eating  amphipods  exposed 
when  the  drift  breaks  up. 

Ainley  (1976)  states  that  "...marine 
biologists  as  a  general  rule  ignore 
birds."  This  viewpoint  is  confirmed  in 
the  case  of  bird-kelp  interactions  and,  as 
further  indicated  by  the  considerable 
speculation  in  this  section  of  the 
profile,  much  remains  to  be  learned  about 
the  relationship  between  kelp  forests  and 
nearshore  bird  populations. 

4.6.2  Marine  Mammals  Introduction.  The  sea  ot- 
ter, gray  whale,  killer  whale,  harbor 
seal,  and  California  sea  lion  (Figure  24) 
are  listed  (North  1971a)  as  the  mammals 
associated  with  the  kelp  forests  of  south- 
ern California  and  northern  Baja  Cali- 
fornia, Mexico,  although  the  sea  otter 
does  not  presently  occur  south  of  Point 
Conception  (Figure  8).  All  of  these 
mammals  do  occur  associated  with 
Macrocystis  pyri  fera  and  Nereocystis 
luetkeana  along  the  central  California 

The  sea  otter  (En hydra  lutris) 
exhibits  the  closest  association  with  kelp 
forests,  potentially  inhabiting  the  kelp 
surface  canopy  and  foraging  throughout  the 
water  column  during  its  entire  life.  Gray 
whales    (Eschrichtius    robustus)    are 

Gray    Whale 

Killer    Whale 

Figure  24.  Marine  mammals  associated  with 
kelp  forests. 

commonly  seen  offshore  from  kelp  forests 
during  their  migrations  along  the  coast, 
and  have  been  observed  to  feed  on  mysid 
shrimp  associated  with  the  kelp.  The 
relationship  of  California  sea  lions 
(Zalophus  cal ifornianus)  and  killer 
whales  (Orcinas  orca)  to  kelp  forests  is 
probably  limited  to  transitory  foraging 
excursions  in  the  kelp.  Harbor  seals 
(Phoca  vitul ina)  are  frequently  seen  in 
kelp  forests  and  feed  on  a  variety  of  kelp 
forest  fishes. 

The  size  of  gray  whale  and  sea  otter 
populations  in  the  northeast  Pacific  was 
drastically  reduced  by  the  early  part  of 
this  century  due  to  human  exploitation. 
Historical  accounts  of  the  aboriginal  and 
commercial  exploitation  of  sea  otters  can 
be  found  in  Kenyon  (1969);  those  of  gray 
whales  in  Rice  and  Wolman  (1971). 
Enactment  of  protective  legislation  for 
otters  in  1911,  and  for  gray  whales  in 
1972,  has  been  instrumental  in  the 
dramatic  recovery  of  both  populations.  As 
these  animals  have  increased  in  numbers 
and  begun  to  inhabit  portions  of  their 
ancestral  range,  their  respective  roles  in 
the  ecology  of  the  kelp  forest  community, 
particularly  that  of  the  sea  otter,  are 
being  elucidated.  Sea  otter  (Enhydra  lutris). 
In  California,  the  preferred  habitat  of 
the  sea  otter  is  a  lush  kelp  canopy  in 
proximity  to  rocky  substrata  with  deep 
crevices  (Woodhouse  et  al.  1977).  Kelp 
forests  dampen  wave  action,  creating  areas 
of  calm  that  serve  as  otter  refuges  from 


winter  storms.  The  forests  may  also  serve 
as  protection  from  predators  such  as  white 
sharks.  If  kelp  surface  canopies  are 
present,  otters  sleep  in  them,  and  are 
often  observed  with  strands  of  kelp  draped 
over  their  bodies,  presumably  to  prevent 
movement  (Kenyon  1969).  Jameson's  (pers. 
comm. )  current  studies  on  sea  otter 
behavior  have  also  shown  a  close 
association  between  sea  otters  and  kelp. 
Otters  are  most  commonly  found  in 
protected  inshore  kelp  canopies  in  central 
California  in  winter,  when  storms  remove 
canopies  in  deeper  water.  Otters 
gradually  move  out  into  the  offshore 
canopies  as  these  reform  in  spring  and 
summer.  After  the  extreme  winter  storms 
of  1982-83,  Jameson  (pers.  comm.)  observed 
that  most  otters  along  the  shore  near  San 
Luis  Obispo  were  inhabiting  the  few  small, 
shallow  stands  of  giant  kelp  that 
remained;  we  observed  similar  behavior  in 
Carmel  Bay. 

Kelp  forests  also  function  as  a 
nursery  area  for  females  with  pups. 
Sandegren  et  al.  (1973)  postulated  that 
females  give  birth  to  pups  while  in  the 
water.  Jameson  (1983)  discovered  a 
mother-pup  pair  hauled-out  on  land  minutes 
after  the  pup  had  apparently  been  born. 
He  hypothesized  that  sea  otters  give  birth 
in  kelp  forests  whenever  possible.  When 
kelp  surface  canopies  are  unavailable, 
however,  birth  may  be  accomplished  on 
land.  In  heavy  seas,  pups  use  kelp 
strands  as  anchors  while  females  forage. 
During  winter  storms  in  central  California 
when  the  kelp  canopy  is  reduced,  increased 
competition  between  mother-pup  pairs  may 
occur  for  space  in  the  available  canopy 
(Sandegren  et  al .  1973) . 

The  diet  of  sea  otters  in  kelp 
forests  consists  of  epibenthic 
invertebrates  commonly  associated  with  low 
intertidal  and  subtidal  rocky  substrata 
with  deep  crevices  (e.g.,  sea  urchins, 
abalone),  and  with  kelp  fronds  (e.g., 
Tegula  spp.,  kelp  crabs;  see  review  in 
Woodhouse  et  al.  1977,  Estes  et  al .  1981). 
Otters  forage  at  depths  to  40  m,  securing 
their  prey  with  their  forepaws,  and 
returning  to  the  surface  to  eat  (Kenyon 
1969).  California  sea  otters  display  a 
unique  type  of  tool-using  behavior  when 
feeding  on  hard-shelled  invertebrates: 
food  items  may  be  pounded  against  a  rock 

held  on  the  otter's  chest  while  floating 
at  the  water's  surface  (Fisher  1939). 
Houk  and  Geibel  (1974)  described  an 
incident  of  a  sea  otter,  underwater, 
pounding  an  attached  abalone  with  a  rock. 

Costa  (1978)  calculated  that  an 
average-sized  otter  must  consume  25%  of 
its  body  weight  daily  to  meet  its  energy 
needs.  Ostfeld  (1982)  studied  the 
foraging  "strategies"  of  a  colonizing 
group  of  otters  in  a  Macrocystis  forest 
off  Point  Santa  Cruz,  California. 
Initially,  red  sea  urchins  were  the 
otter's  major  prey  item.  Kelp  crabs  and 
clams  replaced  urchins  as  major  prey  items 
as  urchins  became  increasingly  scarce. 
Abalone  and  cancer  crabs  were  consistently 
exploited  as  dietary  items  at  relatively 
low  levels.  Other  rocky  substrata  prey 
items  include  snails,  mussels,  octopus, 
chitons,  tubeworms,  limpets,  barnacles, 
scallops,  and  starfish  (Ebert  1968,  Wild 
and  Ames  1974,  Shimek  1977,  Woodhouse  et 
al.  1977,  Estes  et  al.  1981).  Van  Wagenen 
et  al.  (1981)  observed  sea  otters  preying 
on  seabirds. 

Otters  are  able  to  adapt  to  diverse 
environments  (Woodhouse  et  al.  1977).  The 
spreading  fronts  of  the  California 
population  have  successfully  occupied 
sandy  and  silty  bottom  coastal  zones, 
exploiting  Pismo  clams,  gaper  clams,  razor 
clams,  mole  crabs,  and  even  echiuroid 
"worms"  as  prey  (Wild  and  Ames  1974, 
Stephenson  1977,  Hines  and  Loughlin  1980). 
Outside  the  protection  of  the  kelp  canopy, 
the  sea  otter  is  susceptible  to  attacks  by 
the  great  white  shark  (Ames  and  Morejohn 
1980).  Other  than  man  and  parasites,  this 
shark  is  its  only  known  predator  in 
California  waters. 

Before  commercial  exploitation,  the 
range  of  the  sea  otter  extended  in  a 
continuous  arc  from  the  northern  islands 
of  Japan,  along  the  Kamchatka  coastline, 
across  the  Aleutian  Islands  chain,  and 
southward  along  the  west  coast  of  North 
America  into  lower  Baja  California,  Mexico 
(Kenyon  1969).  The  population  southeast 
of  the  Aleutian  chain  was  believed  to  be 
extinct  until  the  discovery  in  1938  of  a 
raft  of  50  to  90  individuals  along  the 
central  California  coast  (Bolin  1938, 
Woodhouse  et  al.  1977).  After  legal 
protection  was  afforded,  the  range  of  the 


sea  otter  extended  at  the  rate  of 
approximately  4  km  annually,  with  a  total 
population  increase  of  5%  per  year  until 
recently  (Wild  and  Ames  1974).  Presently, 
a  population  of  approximately  1,300 
individuals  occupies  a  range  extending  320 
km  along  the  California  coast  from  Point 
Sal,  San  Luis  Obispo  County,  to  Point 
Santa  Cruz,  Santa  Cruz  County  (Estes  and 
Jameson  1983).  However,  there  has  been  no 
apparent  increase  in  population  size  since 
the  late  1960 ' s  (Estes  and  Jameson  1983). 
The  incidental  entanglement  of  otters  in 
commercial  fishing  gear,  particularly  gill 
and  trammel  nets,  may  be  partly 
responsible  for  the  present  stabilization 
in  population  size  (Keating  pers.  comm.). 

Kelp  distribution  and  abundance  can 
be  limited  by  sea  urchin  grazing  (see 
Sections  and  5.5.3);  numerous 
investigators  (Boolootian  1961,  Ebert 
1968,  Benech  1980,  Ostfeld  1982)  have 
observed  otters  colonizing  kelp  forests  in 
central  California  to  prey  preferentially 
on  red  sea  urchins  and  abalone.  Estes  and 
Palmisano  (1974)  asserted  that  sea  otters, 
by  their  removal  of  sea  urchins,  will  have 
a  profound  effect  on  the  structuring  of 
nearshore  communities.  Where  sea  otters 
forage  over  rocky  substrate,  sea  urchin 
densities  will  decrease,  and  if  sea 
urchins  were  limiting  algal  growth,  a 
subsequent  increase  in  macroalgal  biomass 
will  result.  However,  Cowen  et  al.  (1982) 
caution  that  the  sea  otter's  influence 
should  not  be  generalized  as  the  dominant 
factor  structuring  giant  kelp  communities 
in  California.  In  their  study  area, 
physical  factors,  particularly  water 
motion  due  to  winter  storms,  had  a  greater 
effect  than  the  removal  of  urchins  on  a 
nearshore  kelp  community.  A  variety  of 
factors  (storms,  grazing,  other  predators, 
recruitment  events,  etc.)  may  have 
significant  effects  on  giant  kelp 
community  structure  (Foster  1982a;  see 
Chapters  3  and  5),  and  generalizations 
about  the  great  importance  of  the  sea 
otter-sea  urchin  interaction,  based  on 
studies  in  other  geographic  areas  or  in 
sites  disturbed  by  man  in  southern 
California,  may  not  apply  to  the 
heterogeneous  California  coast  (see  also 
Chapter  5). 


(Eschrichtius  robustus). 

Gray  whale 
Gray   whales 

migrate  yearly  from  their  summer  feeding 
grounds  in  the  Bering  and  Chukchi  Seas  to 
their  winter  breeding  grounds  along  the 
coast  of  Baja  California,  Mexico.  Each 
leg  of  the  journey  encompasses 
approximately  10,000  km,  and  takes  between 
2.5  and  3  months  (Rice  and  Wolman  1971). 
In  both  the  southern  and  northern  phases 
of  the  migration,  gray  whales  pass  within 
a  few  km  of  the  California  coastline. 

Scammon  (1874)  noted  that  gray  whale 
cows  with  their  calves  swim  very  close  to 
shore  on  their  northern  migration,  often 
passing  through  kelp  beds.  During  the  era 
of  active  whaling  in  California  (late 
1800s  to  1969),  cow-calf  pairs  were 
observed  only  rarely  on  their  northern 
migration,  and  were  thought  to  use  a  more 
distant  offshore  migrational  route  than 
solitary  whales  (Rice  and  Wolman  1971). 
As  populations  have  increased,  Poole  (in 
press)  has  reconfirmed  Scammon 's 
observation  that  cow-calf  pairs  undertake 
a  nearshore  northern  migration  route, 
while  individual  males  and  females  travel 
a  point-to-point  offshore  route.  Cow-calf 
pairs  pass  along  the  central  California 
coastline  in  April  and  May,  2  months  later 
than  solitary  whales.  They  migrate  along 
an  inshore  route  200  to  400  m  from  shore, 
and  are  often  sighted  along  the  outer 
edges  of  kelp  forests,  or  within  the  kelp 
canopy  itself. 

Poole  (in  press)  recognizes  two 
possible  advantages  gained  by  cow-calf 
pairs  utilizing  a  nearshore  route  that 
passes  near  kelp  communities.  First,  kelp 
forests  may  provide  protection  from 
predation  by  killer  whales.  Baldridge 
(1972)  described  in  detail  the  attack  of  a 
pod  of  killer  whales  on  a  cow-calf  pair 
near  a  kelp  forest  off  Carmel ,  California. 
The  reaction  of  the  cow  and  calf  to  the 
attack  was  to  seek  refuge  in  a  nearby  kelp 
forest.  The  killer  whales  cut  off  the 
calf's  retreat  into  the  kelp.  The  calf 
was  subsequently  killed,  but  the  cow 
escaped  into  the  kelp. 

Kelp  forests  may  also  provide 
potential  food  for  the  nursing  cow.  Gray 
whales  feed  primarily  on  benthic  gammarid 
amphipods  found  in  great  abundance  in 
their  Arctic  feeding  grounds.  It  is 
generally  accepted  that  gray  whales  do  not 
feed  while  migrating  or  during  their 


occupation  of  breeding  areas  in  Baja 
California,  Mexico  (Rice  and  Wolman  1971; 
Oliver  et  al .  1983).  However,  there  is 
now  evidence  that  gray  whales,  while 
migrating,  feed  on  dense  swarms  of  mysid 
shrimp  within  or  along  the  outer  edges  of 
kelp  beds  and  forests  (Wellington  and 
Anderson  1978,  Poole  in  press,  Murison  et 
al.  in  press).  It  may  be  advantageous  for 
a  gray  whale  cow  with  a  dependent  calf  to 
supplement  her  stored  reserves  by  feeding 
upon  the  abundant  mysid  resource 
associated  with  kelp  (Poole  in  press). 

Killer  whale  (Orcinus  orca).  The 
status  and  distribution  of  the  California 
population  of  killer  whales  are  not  known 
(Morejohn  1977).  Killer  whales  feed  in 
small  groups  in  nearshore  regions, 
particularly  near  areas  of  high  marine 
mammal  concentrations  (e.g.,  pinniped 
rookeries;  Rice  1968).  Pods  of  killer 
whales  have  been  sighted  traveling  along 
the  edge  of  kelp  forests  (Daugherty  and 
Schuyler  1979).  Pinnipeds.  Harbor  seal 
(Phoca  vitulus).  Harbor  seals  are  year- 
round  residents  of  embayments,  sloughs, 
and  rivers  along  the  California  coast, 
with  an  estimated  population  of  20,000 
individuals  (Miller  pers.  comm.).  Jones 
(1981)  describes  the  diet  of  harbor  seals 
as  consisting  of  shallow-bottom  fishes 
that  live  near  rock  habitat,  but  they  also 
feed  on  pelagic  fishes  in  many  areas 
(Estes  pers.  comm.).  Greenlings  and  surf- 
perch,  two  common  groups  of  kelp  forest 
fishes  (see  Section  4.5),  were  included  by 
Jones  as  major  prey  items.  Daugherty  and 
Schuyler  (1979)  pointed  out  that  harbor 
seals  resting  in  thick  beds  of  kelp  with 
their  heads  protruding  above  the  surface 
are  often  mistaken  for  sea  otters. 
Although  we  could  locate  no  specific 
reference  to  the  harbor  seal's  association 
with  kelp  beds,  individuals  are  commonly 
observed  while  diving  in  kelp  and  probably 
forage  extensively  in  kelp  forests  when 
these  habitats  are  close  to  seal  haul-out 
areas.  Jameson  (pers.  comm.)  has  even 
observed  a  harbor  seal  partially 
hauled-out  on  a  dense,  floating  canopy  of 
Nereocystis  luetkeana. 

California  sea  lion  (Zalophus  cali- 
fornianus).  The  California  sea  lion 
breeds  on  the  Channel  Islands  of  southern 

California,  along  the  coast  of  Baja 
California,  Mexico,  and  in  the  Gulf  of 
California  during  June  and  July.  During 
the  remainder  of  the  year,  some  75,000  sea 
lions  (Bonnell  pers.  comm.)  inhabit  the 
entire  coastal  region  of  California. 
Groups  of  sea  lions  are  sometimes  seen 
passing  through  kelp  forests  or  foraging 
along  the  kelp  forest  fringe.  Sea  lions 
show  a  preference  for  pelagic  prey  items 
(Jones  1981).  It  is  probable  that  the 
association  of  sea  lions  with  kelp  forests 
is  limited  to  transitory  foraging, 
although  these  animals  are  commonly 
observed  in  kelp  forests  by  divers.  Steller's  sea  cow  (Hydro- 
damalis  gigas).  Giant  kelp  forests  were, 
in  the  past,  probably  also  inhabited  by 
the  now-extinct  Steller's  sea  cow.  This 
huge  (6,000  kg,  over  7  m  long;  Domning 
1978)  herbivorous  mammal  is  believed  to 
have  inhabited  nearshore  areas  from  Baja 
California,  Mexico,  to  Russia.  Probably 
as  a  result  of  hunting  by  aboriginal  man, 
only  an  estimated  2,000  animals  remained 
in  the  remote  portions  of  the  western 
Aleutian  Islands  and  eastern  Russia  by 
1741,  and  the  last  animal  is  believed  to 
have  been  killed  in  1768  (Domning  1978). 

Hydrodamalis  gigas  apparently  did  not 
completely  submerge,  and  fed  on  various 
seaweeds  and  sea  grasses  in  very  shallow 
(probably  1-2  m)  water  (Domning  1978). 
Its  shallow  subtidal  habitat,  lack  of 
diving,  and  slow  movements  made  this 
sirenian  easy  prey  for  hunters.  Dayton 
(1975)  suggested  that  sea  cow  grazing  may 
have  been  important  in  the  evolution  of 
algal  assemblages  in  kelp  forests. 
However,  given  what  is  known  of  the  sea 
cow's  habitat  and  method  of  feeding,  this 
is  arguable.  Although  apparently  never 
observed,  sea  cows  could  have  fed  on 
surface  canopies  in  deeper  water. 

4.7.1  Introduction 

A  variety  of  pathogens  and  parasites 
infect  macro-organisms  in  giant  kelp 
forests,  but  except  for  a  limited  number 
of  cases  reviewed  below,  little  is  known 
of  their  effects  on  host  populations. 


4.7.2  Macroalgae 

Andrews  (1977)  and  Goff  and  Glasgow 
(1980)  recently  summarized  information  on 
seaweed  pathogens,  and  the  latter 
publication  is  a  particularly  compre- 
hensive account.  Perhaps  the  most 
notorious  disease  is  "black  rot"  of 
Macrocystis,  which  is  visible  as  dark 
areas  on  the  margins  of  the  blades.  These 
become  lesions,  and  the  blades  eventually 
disintegrate.  The  symptoms  may  occur 
throughout  large  kelp  stands,  suggesting 
that  the  disease  may  cause  large-scale 
loss  of  plants  (ZoBell  1946).  Scotten 
(1971),  however,  could  not  find  evidence 
of  a  bacterial  or  fungal  cause,  and 
suggested  that  black  rot  is  not  caused  by 
a  pathogen,  but  may  simply  be 
deterioration  associated  with  elevated 
water  temperatures.  Dean  (pers.  comm.) 
observed  extensive  black  rot  and  numerous 
sinking  fronds  in  southern  California  kelp 
forests  in  October  1983,  coincident  with 
the  warm  water  associated  with  the  current 
"El  Nino"  (see  Section  2.3). 

Recent  observations  of  adult 
Macrocystis  pyrifera  isolated  in  a  large 
container  at  Santa  Catalina  Island 
revealed  another  potential  disease  (Gerard 
pers.  comm.).  Blades  (especially  those 
near  the  holdfast)  growing  in  warm,  high 
nutrient  water  developed  numerous  small 
holes  and  eventually  deteriorated.  Dean 
(pers.  comm.)  noted  similar  symptoms  in 
small  Pterygophora  cal ifornica  off  San 
Onofre  in  1983.  The  symptoms  in 
Macrocystis  led  to  the  tentative  name  of 
"shot  hole  disease,"  but  the  cause  is 
unknown.  However,  just  as  in  monocultures 
of  terrestrial  plants,  the  common 
occurrence  in  culture  of  this  hitherto 
rarely  observed  symptom  suggests  that 
other  unanticipated  problems  with  disease 
may  occur  in  future  attempts  to  isolate 
Macrocystis  in  culture  (see  Goff  and 
Glasgow  1980  for  a  review  of  pathogens  in 
other  currently-cultivated  seaweeds). 

Macrocystis  as  well  as  other 
macroalgae  are  inhabited  by  a  diverse 
group  of  potential  pathogenic  organisms 
such  as  nematodes,  algal  and  animal  epi- 
growths,  algal  parasites,  bacteria,  and 
fungi.  Plants  may  be  found  with  tumors 
and  galls  (Andrews  1977,  Goff  and  Glasgow 
1980).  Few  of  these  have  been  observed  to 

cause  severe  damage  to  individuals  in  kelp 
forests,  and  none  has  been  observed  to 
cause  damage  to  populations. 

4.7.3  Invertebrates 

Invertebrate  pathogens  and  parasites 
are  also  common,  and  some  have  significant 
impacts  on  populations.  Pearse  et  al . 
(1977)  reported  a  mass  mortality  of  red 
sea  urchins  (Strongylocentrotus 
franciscanus)  near  Santa  Cruz,  and 
reviewed  other  occurrences  of  this 
phenomenon  in  California.  When  affected, 
the  urchins'  spines  are  no  longer  held 
upright  and  are  eventually  lost,  the 
epidermis  degenerates,  and  the  animal 
dies.  Similar  symptoms  and  widespread 
mortality  have  occurred  recently  in  sea 
urchin  populations  in  Nova  Scotia  (Miller 
and  Colodey  1983).  The  cause  of  the 
disease  in  California  is  unknown;  a 
protozoan  may  be  the  cause  in  Nova  Scotia 
(Miller  and  Colodey  1983).  If  sea  urchin 
grazing  limits  kelp  distribution,  then 
such  a  disease  can  ultimately  result  in 
kelp  forest  enlargement,  as  it  did  at  the 
site  near  Santa  Cruz  (Pearse  and  Hines 
1979),  and  as  it  is  doing  in  Nova  Scotia 
(Pearse  pers.  comm.).  Observations  in 
these  and  other  areas  suggest  that  disease 
may  be  an  important  factor  in  the 
regulation  of  sea  urchin  populations 
(Pearse  pers.  comm. ) . 

Mortality  of  other  echinoderms, 
particularly  the  bat  star  (Patiria 
miniata)  has  been  observed  in  southern 
California,  both  along  the  mainland 
(Schroeter  and  Dixon  pers.  comm.)  and  at 
San  Nicolas  (Harrold  pers.  comm.)  and 
Santa  Catalina  Island  (Gerard  pers. 
comm.).  Similar  mortality  has  occurred  in 
the  Gulf  of  California  (Dungan  et  al. 
1982).  When  the  water  is  abnormally  warm, 
bat  stars  become  covered  with  a  white, 
mold-like  film  and  eventually  die. 
Affected  bat  stars  that  fell  down  steep 
slopes  into  colder  water  at  Santa  Catalina 
Island  apparently  recovered.  Schroeter  et 
al.  (1983)  have  shown  that  P_.  miniata 
predation  may  significantly  alter  the  dis- 
tribution and  abundance  of  white  sea 
urchins  (Lytechinus  anamesus),  and  feeding 
by  the  star  may  also  significantly  affect 
other  populations,  including  plants  (see 
Section  4.4.3  above).  Bat  star 
populations  have  been  nearly  destroyed  by 


disease  in  one  kelp  stand  in  southern 
California  (Schroeter  and  Dixon  pers. 
comm.),  so  this  disease,  like  that 
affecting  sea  urchins,  may  have  important 
community  effects.  The  cause  of  the 
disease  is  unknown. 

The  third  cause  of  death  is 
associated  with  dinoflagellate  blooms  (red 
tides).   Death  in  this  case  may  result 

from    oxygen    reduction 
dinoflagel lates  decomposed. 
(1972)  stated  that  "fish, 
other  marine  life"  have  been 
particular   red   tides 
California,  and 
been  made  at 

when    the 

Fay  et  al . 

lobsters,  and 

killed  during 

in   southern 

similar  observations  have 

least  once  in  central 

California  (Laur  pers.  comm.).  The 
effects  of  these  losses  on  other  organisms 
in  the  kelp  community  are  unknown. 

4.7.4  Vertebrates 

Fishes  are  affected  by  a  number  of 
diseases,  including  the  dinoflagellate 
toxins  above,  but  the  widespread 
occurrence  of  tumors,  lesions,  and  fin  rot 
has  been  particularly  common  in  nearshore 
areas  around  large  ocean  sewer  outfalls 
near  Los  Angeles.  Cross  (1982)  found  that 
11%  of  fishes  caught  in  otter  trawls  in 
this  area  had  fin  rot.  However,  this 
represented  a  decline  from  previous 
percentages,  a  decline  coincident  with  the 
reduction  in  chlorinated  hydrocarbons, 
heavy  metals,  and  organic  matter 
discharged  from  the  sewer.  The  incidence 

of  tumors  and  other  diseases  of  fishes  in 
this  region  is  discussed  by  Mearns  and 
Sherwood  (1977). 

Various  parasites  occur  in  kelp 
forest  fishes  but  the  population 
consequences  of  their  activities  remain 
largely  unknown.  Some  of  these  parasites, 
especially  certain  roundworms,  can  be 
harmful  to  man  if  infected  fish  are  eaten 
raw.  Moser  and  Love  (1978)  reviewed 
parasites  of  marine  fish  in  California, 
and  suggested  methods  for  detecting  and 
destroying  those  harmful  to  man. 

Parasites  may  harm  fishes,  but  they 
can  also  be  used  to  study  fish  movements. 
Some  fishes  with  limited  movements  may 
show  higher  incidences  of  a  particular 
parasite  in  local  populations.  Love 
(1980)  used  such  a  parasite  "tag"  in  his 
innovative  study  of  movements  of  the  olive 
rockfish  (see  Section  4.5  above).  He 
found  that  this  rockfish  moved  little 
between  reefs;  thus  a  particular  reef  can 
be  easily  overfished. 

Numerous  animals  parasitize  marine 
mammals  (see  Dailey  and  Brownell  1971  for 
review).  The  sea  otter,  most  commonly 
associated  with  kelp  forests  (see  Section  above),  has  a  number  of 
acanthocephalan  parasites  (Hennessy  and 
Morejohn  1977).  While  individual  animals 
may  be  seriously  affected  by  some 
parasites,  these  authors  concluded  that 
effects  on  the  sea  otter  population  in 
Cal ifornia  are  small . 


Plate  1A.   Macrocystis  surface  canopy  near 
Santa  Barbara. 

Plate  1C.  Macrocystis  forest  with  numer- 
ous fish  beneath  the  surface  canopy  (cour- 
tesy D.  Reed). 

Plate  IB.   Infra-red 
Macrocystis  (orange) 
(courtesy  California 
and  Game). 

aerial  photograph  of 

canopy  in  Carmel  Bay 

Department  of  Fish 

Plate  ID.   Pelagophycus  porra  at  Santa 
Catalina  Island. 

Plate  IE.   Understory  canopy  of  Ptery- 
gophora  cal  ifornica  (courtesy  S.  Pace). 

Plate  IF.  The  articulated  coralline  alga 
Cal 1 iarthron,  and  the  purple-ringed  top 
shell,  Calliostoma  annulatum. 



Plate  2A.  The  lined  chiton  Tonicella 
1 ineata,  on  an  encrusting  coralline  alga. 
Dark  spots  on  the  coralline  are  openings 
to  polychaete  tubes. 

Plate  2C.   Various  tunicates  and  sponges 
on  a  vertical  wall  within  a  kelp  forest. 

Plate  2E.  Pisaster  giganteus  and  a  group 
of  strawberry  anemones,  Corynactis  cal  i- 
fornica  (courtesy  S.  Webster). 

Plate  2B.   Cup  corals  and  the  cobalt 
sponge  Hymenamphiastra  cyanocrypta. 

Plate  2D.   Red  sea  urchins  surrounded  by 
various  foliose  red  algae. 

Plate  2F.   The  hydrocoral  Al  lopora  cal  i- 
fornica  (courtesy  S.  Webster). 




The  ecosystem  must  first  be  accurately  described  using  proper 
methods  of  sampling  and  measuring  the  relevant  environmental 
variables.  Once  this  is  done,  the  ecologist  looks  for  patterns  of 
correlation  between  the  distribution  and  abundance  of  the  dif- 
ferent organisms  and  their  abiotic  environment.  By  asking  ques- 
tions about  the  causes  of  the  patterns,  answers  suggest 
themselves  which  can  be  formulated  as  testable  hypotheses. 
Then  experiments  can  be  designed  to  test  these  hypotheses. 
Connell  (1974). 


Previous  chapters  have  been  primarily 
descriptive,  discussing  various  biotic  and 
abiotic  factors  associated  with  the 
distribution  and  abundance  of  Macrocystis 
and  other  organisms  in  giant  kelp  forests. 
The  availability  of  light,  nutrients,  and 
suitable  substrata,  temperatures  and  water 
motion  put  broad  limits  on  where  kelp 
forests  might  occur,  but  they  reveal 
little  about  the  mechanisms  and 
interactions  which  structure  these  types 
of  communities.  In  many  cases,  subtidal 
workers  have  substituted  a  rubber  diving 
suit  for  the  tweed  coat  and  gumboots  of 
the  early  intertidal  natural  historian, 
attempting  to  describe  habitats  and  the 
organisms  present  in  terms  of  associations 
and  observed  patterns.  Only  in  relatively 
recent  times  has  the  technology  of  SCUBA 
diving  allowed  researchers  to  explore 
subtidal  communities  in  a  routine  fashion, 
permitting  them  to  identify  the  factors 
and  patterns  that  form  the  basis  of 
experimentally  testable  hypotheses. 
Consequently,  there  are  only  a  few 
published  accounts  of  studies  that  have 
tested  for  the  processes  that  affect  the 

species,  and 

and   abundances 
fewer  still  that 
of  factors. 

of   kelp 
assess  the 

Putatively  important  processes  such 
as  competition  and  grazing  (=  predation  of 
plants  by  animals)  may  have  strong  effects 
in  some  places,  at  some  times.  The 
interactions  between  kelps  and  other 
organisms  may  have  different  effects  at 
various  stages  of  the  life  cycles  of 
plants  (Figure  25).  The  abundances  of 
individual  species  change  along  a  depth 
gradient,  which  may  affect  the  intensity 
of  interactions.  Analyses  of  many  of 
these  problems  are  now  tractable 
experimental ly. 

A  critical  examination  of  the  methods 
used  to  assess  the  important  processes 
that  structure  communities  is  not  unique. 
Currently,  there  is  much  debate  about  the 
importance  of  competition  in  terrestrial 
and  marine  intertidal  communities:  when 
and  where  is  competition  important,  or 
does  it  even  occur  at  all  in  many 
situations  (Connell  1983;  Simberloff  1983; 
see  American  Naturalist  1983,  122(5))? 
When  and  where  is  predation  important? 
Methodological    problems    have    been 


The  Gauntlet  of  Macrocystis  Microscopic  Stages 

will  be  affected  by   light,  water,  motion,  etc.,  that  vary  with   season 


-  avoid  other  Laminarians  on  way  down 

-  avoid  branches  of  Articulated  Corallines 

-  avoid  space  settled  by  other  species 

-  avoid  chemical  inhibition  by  species 



-  avoid  removal  by  water  motion 

-  avoid  entanglement  with  own  species 

-  avoid  competition  with  other  species 

-  avoid  grazers 


-  avoid  overgrowth  and  shading 

by  other  organisms 

-  avoid  grazers 

-  small   echinoids 

-  gastropods 

-  micro-crustarea 

-  Patiria 

-  avoid  being  buried  and  abraded 

by  sediments 




affected  by: 

-  density  of  own  species 

-  density  of  other  species   nearby 

-  developing  canopy 

-  grazers 



-   fertilize 


-  avoid  overgrowth  and  shading 

by  other  organisms 

-  avoid  grazers 

-  avoid  sediments 

Figure  25.   The  gauntlet  of  Macrocystis  life  history  stages, 
affected  by  physical /chemical  factors  that  vary  in  time. 

Survival  will  also  be 

discussed,  along  with  interesting  and 
innovative  approaches  to  experimental 
studies  (e.g.,  Underwood  and  Denley  1984; 
see  Strong  et  al.  1984).  This  debate  is 
particularly  germane  to  subtidal  studies, 
which  are  in  a  relatively  early  stage  of 
experimental  work. 

This  chapter  focuses  on  the  questions 
asked  and  the  hypotheses  proposed 
concerning  the  distribution  and  abundance 
of  Macrocystis ,  the  studies  that  have 
examined  them,  and  the  evidence  for  their 
importance.  Some  of  the  studies  mentioned 
earlier  in  this  review  are  more  critically 
examined   for   details   of  experimental 

design  and  the  conclusions  based  on  them. 
Figure  26  outlines  the  factors  commonly 
cited  as  affecting  one  or  more  of  the  life 
history  stages  of  this  species.  Several 
spatial  and  temporal  scales  are  also 
listed.  Not  all  of  these  hypotheses  are 
presently  capable  of  being  assessed 
experimentally  in  the  field.  Much  of  this 
will  require  innovative  techniques  and 
methods  (for  review  of  current  methods, 
see  Foster  et  al.  in  press). 

Most  subtidal  researchers  are 
logistically  constrained  to  working  at 
relatively  local  sites  along  one  area  of 
coastline,  and  usually  over  a  short  time 


Species  interactions 





may  be  allected  b\ 


I.For  resources 

2.  Interference 

3.  Pre-emption  of  space 


Life  history 

expressed  through 



Other  factors 

also  affected  by 

Water  motion 




Long  term  (5  years) 

Between  local  areas 

Between  years 

Within  local  areas 


Between  depths 

Within  depths 

Figure  26.   Summary  of  important  features  of  kelp  forest  dynamics  and  the  temporal  and 
spatial  scales  at  which  they  occur. 

scale  of  a  few  years  at  most.  The  large 
prominent  surface  canopy  of  Macrocystis 
pyrifera  has  tended  to  obscure  the 
variability  of  the  communities  it 
dominates  at  local  sites.  Kelp  forests, 
however,  may  be  as  variable  within  areas 
as  they  are  among  different  areas  along  a 
coast  (Rosenthal  et  al .  1974,  Foster  et 
al.  1983;  see  Chapter  3).  Experimental 
studies  of  the  factors  producing 
variability  between  and  within  sites  are 
possible  on  relatively  restricted  spatial 
and  temporal  scales. 

Finally,  an  examination  of 
experimental  studies  involving  kelp 
abundances  and  distribution  shows  that  in 
most  cases  only  one  factor  has  been 
assessed,  in  one  place,  at  one  time. 
Factorial  experiments  are  necessary  to 
test  the  relative  importance  of  factors, 
their  interactions,  and  unaccounted  for 
variability.  Many  more  areas  will  have  to 
be  examined  before  any  generalizations 
assume  validity.  In  addition,  many 
studies  suffer  from  pseudorepl ication 
(inferential  statistical  testing  using 
subsamples  from  within  one  "experimental" 
plot  and  one  "control"  plot;  Hurlbert 

1984).  Replication  of  treatments  and 
sites  within  each  area  is  a  powerful  means 
of  assessing  local  variability  (Hurlbert 
1984).  We  do  not  go  into  the  details  of 
experimental  design  and  sampling,  but 
suggest  Underwood  (1981),  Hurlbert  (1984) 
and  Green  (1979)  for  good  discussions  of 


General  hypothesis:  The  distri- 
butional range  of  Macrocystis  is  limited 
by  its  inability  to  survive  higher  temper- 
atures (ca.  20  °C)  and  by  the  inability  of 
gametophytes  to  become  fertile  at  lower 
temperatures  (ca.  5  °C). 

The  most  common  explanation  for 
limits  to  the  geographical  distributions 
of  large  algal  species  is  their  suscepti- 
bility to  temperature.  Susceptibilities 
can  occur  at  several  stages  in  the  life 
histories  of  plants.  The  topic  has  been 
extensively  reviewed  by  Van  den  Hoek 
(1982)  and  is  discussed  in  Section  2.3. 
This  reference  states  that  at  least  six 
different  boundaries  can  be  postulated: 


(1)  the  "northern  lethal  boundary" 
corresponding  to  the  lowest  winter  temper- 
ature at  which  a  species  can  survive;  (2) 
the  "northern  growth  boundary"  correspond- 
ing to  the  lowest  summer  temperature 
which,  over  a  period  of  several  months, 
permits  sufficient  growth  for  plant 
maintenance;  (3)  the  "northern  reproduc- 
tive boundary"  corresponding  to  the  lowest 
summer  temperature  permitting  reproduction 
over  a  period  of  several  months;  and  (4-6) 
the  corresponding  southern  boundaries. 

These  boundaries  have  not  all  been 
investigated  for  Macrocystis  pyrifera  on 
the  west  coast.  The  lethal  southern 
boundary  for  adult  Macrocystis  in 
California  is  thought  to  be  where  20°C 
temperatures  persist  for  at  least  two 
weeks  (North  1971b).  An  established 
population  of  Macrocystis  off  San  Diego 
deteriorated  during  such  a  period.  The 
southernmost  population  of  Macrocystis  off 
Baja  California,  Mexico  is,  however, 
subject  to  higher  temperatures,  and  yet 
has  generally  persisted.  This  highlights 
some  of  the  problems  in  determining 
tolerances  of  individual  species.  Some 
populations  and  some  individuals  will  be 
more  tolerant  than  others  to  environmental 
stresses.  Nevertheless,  Van  den  Hoek 
(1982)  found  broad  correlations  between 
species  tolerances  along  the  coasts  of  the 
Atlantic  Ocean  and  their  distributions 
along  isotherms  for  those  tolerances. 

Because  of  the  variability  in 
community  composition  among  sites,  it  is 
clear  that  testing  for  the  effects  of 
temperature  on  geographic  limits  of 
species  can  only  be  done  indirectly.  Two 
approaches  are  possible:  (1)  laboratory- 
based  studies  on  tolerances,  growth  rates, 
germination  and  survival  of  gametophytes 
and  young  sporophytes;  and  (2)  transplant 
experiments  of  gametophytes  and 
sporophytes  into  similar  habitats  at 
localities  with  different  temperature 

The  main  problems  confronted  in 
comparing  geographic  localities  are  that 
there  are  usually  large  differences  in 
biotic  factors  such  as  the  presence  of 
other  algal  species  and  grazers  (see 
Chapters  3  and  4),  and  also  that 
temperature,  nutrients,  and  light  are 
often  correlated  (Jackson  1977).   It  is 

difficult  to  separate  these  factors  in  the 
field,  but  it  is  relatively 
straightforward  to  measure  them.  Dean  et 
al.  (1983)  and  Dean  and  Deysher  (1983) 
made  continuous  measurements  of 
temperature  and  irradiance  in  the  San 
Onofre  kelp  forest  in  southern  California. 
They  found  that  temperature  and  irradiance 
were  positively  correlated  (Figure  27). 
Successful    natural    recruitment    of 






1 1  - 



12    - 


13    - 


14  - 

15  - 


fin  o/vr  • 


J  \|  U  u  hJ 

16    - 



■    4 








-  3 

-  2 

iyir  * 


18     ■ 

I  ;'        h      Produchc 

T»mp    And  lrr«d<ance 
Required  For  Sporoohyte 
Production  (Above   Line) 

'    i    f1     r~1 — i 


i  f\  ,i ' 














JAN      FEB     MAR     APR    MAY     JUN      JUL     AUG     SEP    OCT      NOV    DEC    JAN 

Figure  27.  Temperature  and  irradiance 
recorded  on  the  bottom  in  a  Macrocystis 
forest  over  a  4-year  period.  Lab  and 
field  studies  indicate  that  Macrocystis 
will  successfully  recruit  only  when  both 
temperature  and  irradiance  are  above  the 
solid  line.  Note  that  temperature  de- 
creases going  up  the  vertical  scale  (from 
Dean  et  al.  1983). 


Macrocystis  sporophytes  was  observed  on 
only  four  occasions  between  1977  and  1981. 
These  episodes  coincided  with  four  of  the 
eight  periods  when  temperatures  were  at  or 
below  16. 3°C ,  and  irradiance  levels  were 
at  or  above  0.4  E/m2/day.  This  study 
indicates  that  temperature  and  light  are 
interactive,  which  may  have  relevance  for 
geographic  distributions.  This  is  similar 
to  conclusions  of  laboratory  studies  of 
Luning  (1980)  for  species  of  Laminaria. 
Appropriate  measurements  of  TTght  and 
temperature  have  not  been  done  in  tandem 
with  recruitment,  growth,  and  survivorship 
studies  in  other  localities.  Such 
studies,  along  with  a  thorough  evaluation 
of  the  biological  differences  among  sites, 
would  provide  important  evidence  for  the 
relative  influence  of  these  factors  on 
both  the  local  and  broad-scale 
distribution  of  large  brown  algae. 


General  Hypothesis:  Severe  water 
motion  (^  1  m/sec)  limits  the  extent  of 
canopy  and  the  distribution  of 

This  hypothesis  is  not  easily 
testable  and  has  not  been  experimentally 
examined.  As  discussed  in  Section  2.6, 
stands  of  Macrocystis  do  not  occur  north 
of  central  California  where  surge 
conditions  are  strong  and  winter  storms 
are  severe.  Surface  canopies  in  the  more 
protected  areas  of  southern  California 
tend  to  fluctuate  in  3-  to  4-year  cycles, 
with  older  plants  being  prone  to  removal 
by  water  motion.  In  central  California, 
however,  winter  storms  tend  to  remove  most 
surface  canopies,  and  there  is  a  marked 
seasonal  change  in  their  extent.  On  a 
local  scale,  North  (1971b)  suggested  that 
the  shoreward  depth  limit  of  Macrocystis 
is  determined  by  surge  conditions. 

Severe  winter  storms  were  associated 
with  the  recent  El  Nino  conditions 
(1982-83)  along  the  entire  coast  of 
California.  These  storms  removed  most  of 
the  canopy  plants  at  Point  Loma  in 
southern  California,  with  the  greatest 
mortality  of  plants  in  the  shallowest  (12 
m)  water  (Dayton  and  Tegner  1984b).  In 
contrast,  at  Stillwater  Cove  in  central 
California,  virtually  all  Macrocystis 
plants  were   removed  by  these   storms 

(Schiel  and  Foster,  unpublished  data).  In 
both  cases,  many  Macrocystis  and 
understory  kelps  eventually  recruited. 

Except  for  abrupt  mortality  of  plants 
due  to  storms,  the  factors  associated  with 
large-scale  phenomena  such  as  El  Ninos  are 
generally  impossible  to  separate,  however. 
Water  motion  is  seasonally  severe  while 
temperatures  are  higher  and  nutrients 

The  observations  of  Ebeling  et  al. 
(MS.)  on  a  reef  near  Santa  Barbara 
indicate  that  severe  storms  can  have 
opposing  effects  on  kelp  communities, 
depending  on  algal  abundances  and  sea 
urchin  behavior  prior  to  and  after  the 
disturbance  (see  discussion  in  Section 
3.5).  As  with  many  studies,  a  possible 
complicating  factor  is  the  lack  of 
knowledge  about  the  intensity  of  algal 
spore  settlement.  Sea  urchin  foraging 
behavior  may  not  have  changed  after  the 
first  storm  had  there  been  a  large 
settlement  of  spores  and  subsequent  large 
recruitment  of  algae.  Nevertheless,  this 
observational  study  indicates  that  water 
motion,  sea  urchin  behavior,  and  kelp 
recruitment  are  related. 


5.4.1  Depth  Distribution 

General  Hypothesis:  The  depth 
distribution  of  kelp  plants  is  limited  by 
the  abiotic  factors  of  light  and 

Some  of  the  main  problems  faced  by 
subtidal  workers  are  the  differences 
between  areas  and  depths  in  physical  and 
biological  factors,  and  also  the 
differences  in  levels  of  these  factors 
among  areas.  Intertidal  studies  provide 
the  best  examples  of  patchiness  in  the 
occurrence  of  organisms  within  and  between 
areas,  and  experiments  to  determine  how 
this  patchiness  originates  and  is 
maintained.  A  particularly  thorough 
quantitative  survey  of  intertidal  areas  in 
eastern  Australia  showed  that  there  were 
broadly  overlapping  vertical  distributions 
of  species,  which  were  partially 
determined  by  exposure  and  substratum 
heterogeneity  (Underwood  et  al.  1983). 
Species  from  different  levels  on  the  shore 


have  different  physiological  tolerances  to 
regimes  of  light,  temperature  and  exposure 
(e.g.,  Quadir  et  al .  1979).  Even  so, 
individual  algal  species  may  not  occupy 
the  zone  where  they  grow  best  (e.g., 
Foster  1982b).  Detailed  experimental 
studies  examining  these  types  of 
interactions  have  rarely  been  done  in 
subtidal  algal  forests. 

Within  sites,  it  has  been  observed 
worldwide  that  subtidal  algal  assemblages 
fall  into  broad  depth  zones  (Kain  1963, 
Neushul  1965,  Mann  1972a,  Choat  and  Schiel 
1982),  and  this  is  generally  the  case  for 
Macrocystis  communities  (see  Chapter  3). 
Most  of  the  physical  and  biotic  factors 
discussed  in  Chapters  2  and  3  will  change 
gradually  along  a  depth  gradient  within 
any  one  site.  For  example,  the  density  of 
kelp  stands  usually  decreases  at  depths 
beyond  ^  20  m,  leaving  isolated  plants  at 
greater  depths  (DeVinny  and  Kirkwood  1974; 
see  Chapter  1).  The  pattern  of  distri- 
bution of  physical  factors  can  also  be 
quite  variable.  While  light  attenuation 
occurs  with  depth,  it  may  also  be  affected 
by  water  clarity  and  the  presence  of  algal 
canopies  (see  Section  2.4).  As  a 
consequence  of  changing  variables  and  the 
physiological  tolerances  of  algae,  the 
demography  of  species  and  composition  of 
algal  stands  also  change  with  depth. 

The  effects  of  depth-associated 
factors  on  algal  production  have  been 
approached  in  several  ways.  North  (1971c) 
measured  the  growth  rates  of  three  young 
Macrocystis  fronds  on  each  of  four  plants 
over  a  period  of  39  days  at  depths  of  8  m 
and  24  m  on  the  edge  of  the  Carmel 
submarine  canyon.  He  found  little 
difference  among  elongation  rates  of 
fronds,  and  concluded  that  the  influence 
of  depth  on  growth  rates  of  young  fronds 
is  probably  slight.  Sample  sizes  were 
small  in  this  study,  and  only  young  fronds 
on  older  plants  were  measured.  Gerard 
(1976)  found  that  within  one  site  in 
central  California,  the  variation  in 
growth  rates  was  extremely  high  from  frond 
to  frond,  even  for  fronds  which  were 
initially  of  equal  size  and  which  were 
measured  over  the  same  time  interval. 

Dean  et  al .  (1983)  at  the  Marine 
Review  Committee  kelp  ecology  project  in 
southern  California  have  done  the  most 

innovative  and  thorough  research  to  date 
examining  factors  that  affect  the 
production  of  Macrocystis  sporophytes  from 
gametophytes.  Their  experiments  will  be 
discussed  in  detail  in  the  next  section. 
Of  relevance  to  the  depth  distribution  and 
abundance  of  Macrocystis,  however,  were 
their  experiments  that  assessed  the 
production  of  sporophytes  at  different 
depths.  They  attached  ropes  containing 
cultured  gametophytes  at  different  depths 
along  a  suspended  cable  (Figure  28).  The 


a  =  Floating  PVC  frame 

b  =  Plexiglass  plates  holding  pieces  of 

nylon  rope  containing  gametophytes 
c  =  Surgical  tubing  with  stainless  steel 

hooks  used  to  attach  plates  to  frame 
d  =  Sediment  tube 
e  =  Irradiance  sensor 
f  =  Irradiance-temperature  integrator  and 

g  =  Stainless  steel  and  safety  cable 
h  =  Iron  anchor  plate 

Figure  28.  Field  station  used  for  Macro- 
cystis pyrifera  gametophyte  outplants 
(Dean  et  al.  1983). 


lowest  ropes  were  on  the  bottom,  with 
replicates  at  2,  4,  and  6  m  above  the 
bottom.  They  recorded  the  density  of 
sporophytes  produced  from  these  cultures, 
and  measured  temperature  and  irradiance 
daily  and  total  nitrogen  weekly.  Nitrogen 
levels  were  generally  higher  on  the  bot- 
tom, and  lowest  at  6  m  off  the  bottom. 
Temperatures  during  August  -  October  were 
lowest  on  the  bottom  and  highest  at  6  m, 
but  differences  were  slight  between  depths 
during  October  -  January.  Irradiance  was 
invariably  lowest  on  the  bottom,  and  pro- 
gressively higher  at  the  shallower  depths. 
Temperature  alone  accounted  for  a  rela- 
tively high  proportion  of  the  variance  in 
sporophyte  density  at  all  depths  (48%). 
Irradiance  explained  a  significant  portion 
of  the  variance  in  sporophyte  density  for 
all  treatments  combined,  but  was  more 
important  for  bottom  substrata.  This  was 
because  light  regimes  on  the  bottom  were, 
at  times,  below  critical  irradiance 
levels.  Sedimentation  levels  also  had  a 
significant  effect,  being  more  pronounced 
on  the  bottom  treatments. 

A  surprising  result  of  these 
experiments  was  that  there  were  not 
significant  correlations  between  nitrogen 
levels  and  the  production  of  sporophytes. 
Several  outplants  of  gametophytes  produced 
high  densities  of  sporophytes  despite  low 
levels  of  nitrogen  (0.2  -  1.0  ug-at/1). 
This  lack  of  correlation  was  attributed  to 
the  fact  that  the  outplants  were  within  a 
narrow  range  of  critical  levels  at  all 
times,  and  that  weekly  measurements  of 
total  nitrogen  may  be  too  coarse  a 
measurement  to  detect  effects  on  settled 

These  experiments  indicate  that  even 
relatively  small  differences  in  depth  may 
have  important  effects  on  gametophyte 
growth,  fertility,  and  the  production  of 
sporophytes.  Critical  thresholds  in 
temperature  and  irradiance  may  be 
approached,  while  levels  of  sedimentation 
may  be  correlated  with  particular  depths. 
These  sorts  of  experiments  which  assess 
the  performance  of  small  plants  while 
monitoring  the  physical  environment  are 
critical  to  an  understanding  of  broad 
zonational  patterns.  The  fact  that  larger 
sporophytes  grow,  and  apparently  do  well 
in  deeper  areas  at  some  sites,  reveals 
little  about  how  plants  come  to  be  in 

those  larger  size  categories.  Gameto- 
phytes and  young  sporophytes  must  cope 
with  the  physical  regimes  of  the 
micro-sites  in  which  they  settle,  in  much 
the  same  way  as  do  terrestrial  plants 
(e.g.,  Harper  1977).  The  logistics  of 
altering  and  controlling  physical  regimes 
at  this  scale  have  not  been  worked  out  for 
field  studies,  but  the  experimental/ 
correlative  approach  used  by  Dean  et  al . 
(1983)  holds  much  promise. 

5.4.2  Variability  Within  Depths 

General  Hypothesis:  The  variability 
in  levels  of  temperature,  light  and  nutri- 
ents at  the  same  depth  within  a  locality 
results  in  the  patchy  distribution  and 
variable  abundance  of  algae. 

There  are  no  field  studies  that 
conclusively  show  the  effects  of 
temperature,  light,  and  nutrients  on  any 
life-history  stage  of  Macrocystis. 
Experimental  studies  have  not  been 
feasible  because  of  the  difficulty  in 
controlling  the  levels  of  these  correlated 
factors  in  the  field.  For  example,  Luning 
(1980)  found  that  the  total  amount  of 
light  needed  for  gametogenesis  in 
Laminaria  increased  exponentially  as 
temperature  increased.  Dean  et  al .  (1983) 
were  able  to  quantify  this  in  field 
experiments.  Macrocystis  spores  were 
settled  onto  small  ropes  in  the 
laboratory,  and  grown  to  the  gametophyte 
stage  before  outplanting  to  the  field. 
The  densities  of  the  sporophytes  that 
eventually  appeared  were  determined,  while 
temperature  and  irradiance  were  measured 
with  jijn  situ  sensors  and  integrating 
recorders.  They  found  that  there  were 
threshold  levels  of  light  and  temperature 
for  the  production  of  different  densities 
of  sporophytes  (Figure  29).  For  example, 
no  sporophytes  were  produced  above  a 
temperature  of  17.6  °C  or  below 
irradiance  levels  of  0.3  E/m2/day.  To  get 
dense  recruitment  (>  50  sporophytes/cm2) , 
temperatures  were  below  16.3  °C,  and 
irradiance  above  0.4  E/m2/day.  Higher 
irradiance  levels  (1  E/m2/day)  were 
required  for  production  of  higher 
densities  of  sporophytes  as  temperatures 
approached  16  °C.  However,  recent 
laboratory  experiments  indicate  there  is 
little  interaction  between  light  and 
temperature  if  nutrients  are  adequate. 


(J  < 

Z  Q 

<  ? 

Q  E 



-.*  50   SPOROPHYTES/    cm2 

.  '50  SPOROPHYTES/   cm2 

13  14  15  16  17 


Figure  29.  Irradiance-temperature  re- 
sponse surface  for  Macrocystis  pyrifera 
sporophyte  recruitment.  Sporophytes 
counted  on  sections  of  rope  initially 
inoculated  with  spores  in  the  laboratory. 
When  spores  developed  into  gametophytes, 
the  ropes  were  put  in  the  field  on  the 
apparatus  shown  in  Figure  28. 

Since  temperature  and  nutrients  are 
inversely  correlated  (Section  2.5),  these 
laboratory  results  suggest  that  it  is  the 
light-nutrient  interaction  that  is 
important  in  the  field  (Deysher  and  Dean 
pers.  comm.). 

Different  sediment  loads  could  lessen 
the  production  of  sporophytes  by  reducing 
irradiance  levels  below  the  compensation 
irradiance  point  (Table  1).  Gametophytes 
were  not  killed  by  sediment,  but  failed  to 
grow.  In  another  study,  DeVinny  and  Volse 
(1978)  found  that  sediment  cover  of 
107  mg/cm2  (0.45  mm  thick)  could  reduce 
gametophyte  survival  by  90%.  These 
results  are  similar  to  those  of  Norton 
(1978),  who  found  that  a  covering  of 
sediment  reduced  light  levels  below  the 
growth  compensation  point  for  the  kelp 
Sacchariza  polyschides.  Sediment  also 
affects  scour,  nutrients,  and  micrograzer 
activity  as  well  as  light. 

The  availability  of  nutrients, 
particularly  nitrogen,  can  affect  the 
growth  of  macro-algae  (see  Section  2.5). 
Some  species  of  large  algae  can  maintain 
growth  during  periods  of  low  ambient 
nutrients  by  building  internal  nitrogen 
reserves.  In  the  case  of  Macrocystis 
pyrifera ,  sporophyte  tissue  may  have  a 
nitrogen  level  10,000  times  that  of  the 
external  supply  (Gerard  1982b).   Wheeler 

and  North  (1981)  found  that  N03"  varied 
seasonally  in  inshore  waters,  and  that 
growth  rates  of  fronds  were  also  seasonal. 
However,  there  was  no  clear  correlation 
between  growth  rates  and  ambient  N03  . 
Gerard  (1982b)  tested  the  effect  of 
nitrogen  depletion  on  growth  rates  of 
fronds  j_n  situ  by  moving  a  plant  from  an 
inshore  kelp  forest  to  an  offshore  area 
with  a  lower  nitrogen  environment.  The 
transplant  was  moored  at  a  similar  depth 
to  the  offshore  site  (^  7  m).  She  found 
that  fronds  maintained  growth  for  two 
weeks,  presumably  as  a  result  of  internal 
nitrogen  reserves,  but  that  growth  rate 
decreased  in  the  third  week.  Despite  the 
relatively  small  nitrogen-storage  capacity 
of  Macrocystis,  she  concluded  that 
nitrogen  saturation  is  uncommon  in 
southern  California  kelp  forests. 

Dean  et  al.  (1983)  did  two  types  of 
experiments  to  test  for  the  effects  of 
nitrogen  levels  on  sporophyte  production. 
In  the  gametophyte  outplant  experiments 
described  earlier,  nitrogen  levels  in  the 
water  column  were  measured.  There  was  no 
correlation  between  the  production  of 
sporophytes  and  nitrogen  levels, 
suggesting  that  nutrients  play  a 
relatively  minor  role  in  recruitment  when 
other  factors  such  as  light,  temperature, 
and  sedimentation  are  considered. 
However,  temperature  and  nutrients  are 
highly  correlated,  and  the  work  of 
Zimmerman  and  Kremer  (1984)  indicates  that 
nutrients  must  be  measured  at  shorter  time 
intervals  than  in  these  experiments.  Dean 
et  al.  (1983)  also  did  nitrogen  addition 
experiments  to  assess  the  effects  on 
sporophyte  production.  Racks  of 
gametophytes  were  situated  above  trays  of 
fertilizer,  rendering  the  nitrogen 
concentration  in  the  vicinity  of  the 
outplants  greater  than  ambient.  In  these 
experiments,  fertilizing  the  substrata  did 
increase  sporophyte  recruitment.  They 
also  found  that  the  plates  on  the  bottom 
showed  a  greater  increase  in  nitrogen  than 
those  higher  in  the  water  column,  probably 
because  of  higher  current  velocities  near 
the  surface  which  diffused  the  fertilizer. 
This  can  also  be  the  case  for  ambient 
nitrogen,  with  vertical  stratification  and 
high  N03"  concentrations  only  near  the 
bottom  (Gerard  1982a).  In  this  case,  the 
interaction  between  nutrients  and  water 
currents  was  important. 


Gerard  (1982c)  also  found  evidence 
that  at  high  concentrations  of  N03"  (25 
uM),  nutrient  uptake  was  saturated  at 
relatively  low  current  velocities  (2.5 
cm/sec).  Furthermore,  she  found  that 
water  surge  and  movement  of  plant  surfaces 
in  the  water  column  were  sufficient  to 
saturate  uptake,  even  in  a  dense 
Macrocystis  forest  with  calm  sea 
conditions  and  low  current  velocity. 

Nutrients   may, 
different  effects  on 
stages  of  plants,  and 
related   to   season, 

therefore,   have 

the  various  life 

this  may  also  be 

stratification   of 

nitrogen,  and  water  motion. 

The  effects  of  light,  temperature, 
nutrients,  and  their  interactions  have 
only  just  begun  to  be  studied.  Better 
field  studies  must  be  devised  which  can 
measure  variability  at  different  scales. 
For  example,  nutrients  may  have  effects  on 
a  small  scale  within  a  kelp  forest;  there 
may  also  be  wery  broad-scale  effects  over 
portions  of  the  forests,  or  the  entire 
kelp  stand.  Fronds  on  a  single  plant  show 
variability  in  growth  rates  and  nutrient 
uptake,  but  there  is  also  variability 
among  plants  of  the  same  age,  exposed  to 
similar  environmental  conditions. 
Experiments  must  be  able  to  quantify  these 
various  levels  of  variability.  Also, 
there  is  a  need  for  careful  controls  with 
which  to  compare  translocated  or 
experimental  kelp  plants. 

One  type  of  experiment  needed  is  a 
laboratory  study  examining  different 
levels  of  light,  temperature,  and 
nutrients  (see  Table  11).  Such  a  design 
will  allow  some  measure  of  main  effects 
and  the  importance  of  interactions.  This 
experiment  is  currently  being  done  by 
Deysher  and  Dean  (pers.  comm.). 

These  are  central  issues  in  the 
controversy  of  what  produces  "good  years" 
and  "bad  years"  for  Macrocystis.  Why  is 
recruitment  greater  at  some  times  and  why 
are  canopies  more  lush  in  different  years? 


5.5.1  Canopy  Removals 

General  Hypotheses:  (1)  Competitive 
interactions  among  species  affect  the 
local-scale  distribution  and  abundances  of 
individual  species.  (2)  Bare  primary 
substratum  significantly  increases  the 
recruitment  of  large  brown  algae. 

The  most  common  method  used  to 
determine  the  effects  of  one  algal  species 
on  another  is  the  selective  removal  of 
algal  canopies  and  the  subsequent 
recording  of  which  species  either 
persisted  in  or  recruited  to  the  areas. 
Dayton  (1975)  removed  canopies  of  several 
species  at  different  depths  at  a  site  in 
Alaska.  Five  hypotheses  were  tested,  each 

Table  11.  Outline  of  an  example  of  a  factorial  laboratory  experiment  to  assess  the 
importance  of  light,  temperature  and  nutrients,  and  their  interactions,  on  gametophyte 
growth,  fertility  and  the  production  of  sporophytes.  The  design  uses  three  levels  for 
each  factor:  nutrients,  light,  and  temperature.  Number  of  replicates  determined  from 
initial  trials  and  desired  statistical  power. 


Nutrients  1 

Nutrients  2 

Nutrients  3 

Light        Light  1   Light  2   Light  3     Light  1   Light  2   Light  3     Light  1   Light  2   Light  3 
Temperature   Tl  T2  T3  Tl  T2  T3  Tl  T2  T3    Tl  T2  T3  Tl  T2  T3  Tl  T2  T3    Tl  T2  T3  Tl  T2  T3  Tl  T2  T3 
Replicates  1. 

2.    (for  each  T) 



relating  to  the  effects  of  one  laminarian 
species  (or  groups  of  them)  on  another. 
His  experiments  indicated  that  the  species 
forming  a  surface  canopy,  Alaria 
f istulosa,  was  not  a  competitive  dominant 
because  other  laminarian  species  did  not 
invade  clearances  when  this  canopy  was 
removed.  Canopies  of  Laminaria  spp. , 
however,  appeared  to  preclude  the 
recruitment  of  Alaria.  The  rhizoidal 
growth  pattern  of  I.  longipes  ensured  that 
relatively  rapid  vegetative  growth  would 
allow  this  species  to  reform  a  canopy 
quickly,  and  so  exclude  other  species  from 
invasion.  Two  other  canopy  removals 
indicated  that  Agarum  cribosum  had  little 
effect  on  other  species,  but  that  its 
cover  increased  when  Laminaria  spp.  were 

These  experiments  clearly  show  that 
canopies  of  individual  species  affect 
other  species.  The  nature  of  these 
effects,  however,  is  not  clear. 
Presumably,  canopy  effects  were  the  result 
of  light  inhibition  to  understory  species 
(see  Section  2.4).  Canopies  may  also 
impede  the  arrival  of  propagules  to  the 
substratum.  One  of  the  main  problems, 
however,  was  the  lack  of  information  about 
reproduction  for  individual  species.  The 
apparent  failure  of  some  species  to 
recruit  successfully  and  the  success  of 
other  species  could  be  a  reflection  of  the 
seasonal  occurrence  of  propagules,  which 
may  not  have  been  available  for  some 
species  at  the  time  of  the  clearances.  In 
addition,  percentage  cover  of  canopies  was 
used  as  a  measure  of  abundance,  and  it  was 
not  clear  whether  plants  that  remained 
after  clearances  of  one  species  increased 
in  size,  or  whether  significant 
recruitment  occurred. 

Many  intertidal  studies  have  shown 
that  free  space  is  a  major  requirement  for 
successful  recruitment  of  sessile  species 
(e.g.,  Dayton  1971,  Connell  1975).  This 
is  probably  the  case  for  subtidal  regions 
as  well,  although  there  is  little 
experimental  evidence  for  this  in 
Macrocystis  forests.  Sessile  organisms, 
particularly  algae  such  as  articulated 
corallines,  fleshy  red  algae  and  stipitate 
laminarians,  may  impede  spore  fall  from 
larger  plants,  may  already  occupy 
available   substrata,   may   have   toxic 

effects  on  settling  spores,  and  may  reduce 
light  levels  below  threshold  values  for 
spore  development. 

Field  experiments  by  Reed  and  Foster 
(1984)  have  shown  that  a  combination  of 
these  effects  can  be  important  to  kelp 
recruitment  in  central  California.  They 
experimentally  removed  canopies  of  over- 
and  understory  plants:  Macrocysti  s , 
Pterygophora,  articulated  corallines,  and 
encrusting  corallines.  The  most  abundant 
understory  kelp  in  the  forest, 
Pterygophora,  reduced  light  levels  to  the 
substratum  by  up  to  90%.  Removal  of  this 
species  resulted  in  a  higher  recruitment 
of  kelp  relative  to  control  areas. 
Clearance  of  articulated  and  encrusting 
corallines,  leaving  patches  of  bare 
substratum,  did  not  yield  more  recruits. 
Lower  recruitment  occurred  in  areas  where 
the  branches  of  articulated  corallines 
were  present,  suggesting  that  the  branches 
themselves  impede  spore  fall  and 
subsequent  development,  or  that  they  may 
severely  reduce  irradiance  to  the 
substratum.  Reed  and  Foster  (1984) 
concluded  that  the  major  factor  affecting 
recruitment  was  the  reduction  of 
irradiance  caused  by  the  Pterygophora 

This  is  the  most  thorough  set  of 
experiments  yet  published  involving 
manipulations  of  algal  abundances  in 
Macrocystis  forests.  Most  combinations  of 
factors  (i.e.,  the  presence  and  absence  of 
each  canopy)  were  used.  A  balanced 
experimental  design,  however,  would  have 
allowed  statistical  tests  of  all  factors 
and  their  interactions,  thus  providing 
stronger  evidence  for  their  conclusions. 

Pearse  and  Hines  (1979)  cleared  a 
Macrocystis  canopy  from  a  20  x  10  m  plot 
and  left  one  area  uncleared  as  a  control 
in  a  kelp  forest  off  Santa  Cruz, 
California.  After  3  months,  significantly 
more  laminarians,  of  several  species, 
recruited  into  the  cleared  plot.  This 
difference  was  attributed  to  light 
inhibition  caused  by  the  intact 
Macrocysti  s  canopy.  Light  measurements 
indicated  that  only  about  0.2%  of  surface 
light  reached  the  bottom  under  the  canopy, 
while  3.8%  reached  the  bottom  in  the 
cleared  plot.  The  long-term  effects  of 
this  differential  recruitment  were  not 


Again,  this  study  suggests  the 
importance  of  light  to  successful  algal 
recruitment,  but  suffers  from  having  only 
one  experimental  plot  and  one  control  ,  and 
the  lack  of  separating  other  factors  such 
as  the  effects  of  understory  species. 

A  different  result  occurred  in  a  kelp 
forest  in  southern  Chile.  Santelices  and 
Ojeda  (1984a)  cleared  a  Macrocystis  canopy 
from  a  5  x  50  m  transect.  The  dominant 
understory  plant,  Lessonia  flavicans, 
increased  in  biomass  in  the  non-removal 
area  but  most  other  permanent  members  of 
the  community  did  not  change  in 
distribution.  The  method  of  removing  the 
canopy,  however,  was  different  than  in 
other  studies.  Plants  were  cut  1  m  below 
the  sea  surface,  rather  than  immediately 
above  the  holdfast.  The  senescence  of  cut 
fronds  could  have  had  an  adverse  effect  on 
Lessonia  in  the  removal  area.  Recruitment 
was  not  specifically  recorded  in  this 
study,  but  there  appeared  to  be  a 
qualitatively  different  response  to  canopy 
removal  in  this  southern  kelp  forest 
depauperate  in  laminarian  species. 

Kastendiek  (1982)  examined  some 
interactions  among  three  algal  species  in 
a  shallow  portion  of  a  Macrocystis- 
dominated  community  at  Santa  Catalina 
Island  in  southern  California.  He  found 
that  two  species  were  narrowly  zoned  with 
depth:  Halidrys  dioeca  (Fucales)  occurred 
abundantly  at  0.5  m  and  1.9  m  below  MLLW, 
with  Eisenia  arborea  (Laminariales) 
occupying  three  intermediate  depths  (0.8, 
1.2  and  1.5  m).  The  third  species,  the 
red  alga  Pterocladia  capil lacea,  was  most 
abundant  beneath  Eisenia  canopies.  By 
selectively  removing  each  species, 
Kastendiek  (1982)  found  that  if  Eisenia 
was  removed,  Halidrys  could  invade 
intermediate  depths  by  growing 
adventitiously  and  preempting  space.  If 
both  Hal idrys  and  Eisenia  were  removed, 
Pterocladia  was  able  to  occupy  free  space. 
Thus,  Eisenia  appeared  to  be  the 
competitive  dominant  at  intermediate 
depths  because  its  dense  canopy  excluded 
Halidrys.  This,  in  turn,  allowed 
Pterocladia  to  occupy  the  space  beneath. 
Two  other  factors  were  cited  as  important 
to  the  coexistence  of  these  species. 
Large  storms  had  a  differential  effect  on 
the  species,  removing  most  Eisenia  plants 
in  some  areas  while  leaving  Hal idrys 

intact.  Differential  recruitment  was  also 
important.  Eisenia  was  able  to  recruit 
beneath  Hal idrys,  yet  even  when  free  space 
was  available  at  all  depths,  Eisenia  had 
few  recruits  above  and  below  the  zone  (1.2 
m)  where  adult  plants  were  most  abundant. 
The  relative  recruitment  failure  in  the 
lower  area  was  probably  not  due  to 
physiological  restrictions  because  Eisenia 
adults  are  very  abundant  at  depths  to  25 
m.  In  this  case,  the  limited  dispersal  of 
algal  spores  or  the  differential  survival 
of  spores  could  be  important  factors. 

5.5.2  Density  of  Macrocystis  Stands 

Hypothesis:  Recruitment  and  growth 
at  high  densities  has  an  adverse  effect  on 
the  growth,  reproduction,  and  survival  of 
Macrocystis  plants. 

Evidence  from  many  terrestrial 
studies  suggests  that  individual  plants  in 
dense  stands  should  exhibit  lower  growth, 
reproduction,  and  survivorship  relative  to 
plants  in  similar  environments  at  lower 
density  (Harper  1977).  The  fact  that 
large,  essentially  monospecific 
aggregations  of  large  brown  algae  commonly 
occur  worldwide  suggests  that  there  might 
be  advantages  to  plants  in  denser  stands, 
in  some  situations.  There  is  evidence 
both  for  and  against  adverse  effects  to 
plants  in  high  density  algal  populations. 
Schiel  and  Choat  (1980)  found  that  two 
subtidal  species  in  New  Zealand,  Ecklonia 
radiata  and  Sargassum  sinclairii ,  had  the 
largest  plants  in  dense,  single-species 
stands  on  one  semi-exposed  reef.  These 
plants  were  of  the  same  age  and  in  an 
apparently  similar  habitat,  although 
differences  among  local  sites  (boulders) 
may  have  been  important.  Cousens  and 
Hutchings  (1983)  reached  different 
conclusions  for  stands  of  brown  algae  in 
Nova  Scotia.  They  found  that  large  plants 
could  occur  at  low  density,  and  concluded 
that  water  motion  was  the  most  important 
factor  determining  size  and  morphology. 
Their  evidence  is  equivocal,  however, 
because  ages  of  plants  were  not  known,  and 
plants  were  in  different  habitats  on  the 
shore.  Black  (1974)  found  that 
survivorship  was  density-dependent  for 
recruits  of  Egregia  laevigata 
(=  menziesii ) ,  but  that  this  was  not  the 
case  after  plants  were  three  months  old. 


There  is  some  information  on  density 
effects  for  Macrocystis.  North  (1971c) 
used  three  stands  of  different  densities 
to  examine  growth  rates  of  fronds.  He 
found  that  the  stand  at  highest  density 
had  plants  which  grew  slightly  faster  than 
those  at  other  densities,  but  attributed 
this  result  to  unknown  "localized 

Neushul  and  Harger  (in  press)  planted 
adult  Macrocystis  (mean  size  of  25  fronds 
per  plant)  at  different  densities  on  a 
test  farm  near  Santa  Barbara,  California. 
The  densities  used  were  1  plant/m2,  1 
plant/4  m2  and  1  plant/16  m2.  The  results 
indicated  that  plants  at  the  lowest 
density  had  the  most  fronds  and  greatest 
weight  after  a  year,  while  the  highest 
density  plants  fared  the  poorest.  Their 
results  suggest  that  shading  in  the  denser 
parts  of  the  stand  caused  the  poorer 
growth.  Possible  complicating  factors  in 
this  experiment  were:  (1)  the  initial  use 
of  adult  plants,  which  may  already  have 
adapted  to  a  particular  growth  regime;  (2) 
the  logistic  constraint  of  using  only  one 
small  experimental  plot  (0.24  hectares) 
with  the  different  densities  being 
contiguous;  and  (3)  the  placement  of  low 
and  medium  density  plants  toward  the 
outside  of  the  stand  where  peripheral 
light  may  have  affected  growth.  Their 
experiment,  however,  forms  a  useful  basis 
for  selecting  planting  densities  for  the 
purpose  of  mariculture  (see  Chapter  6). 

Mortality  may  also  be  affected  by  the 
density  of  stands.  Work  in  both  central 
and  southern  California  has  indicated  that 
the  major  source  of  mortality  for  large 
Macrocystis  plants  is  entanglement  with 
drifting  plants  (Rosenthal  et  al .  1974, 
Gerard  1976).  Large  bundles  of  drifting 
plants  may  accumulate  and  remove  more 
plants  from  the  kelp  forest  during  periods 
of  increased  water  motion. 

Intraspecific  competition  for  light, 
nutrients,  and  space  may  prove  to  be 
important  in  large  brown  algal  systems. 
Testing  for  these  effects  requires 
experiments  which  control  for  the  ages  of 
plants,  habitats,  depths,  and  localized 
factors  associated  with  sites.  These 
experiments  can  take  the  form  of  thinning 
experiments,  whereby  areas  with  high 
recruitment  have  treatments  thinned  to 

lower  densities.  High  recruitment  into  an 
area  indicates  that  it  is  suitable,  at 
least  for  the  initial  life  stages  of  the 
alga.  If  different  density  treatments  are 
contained  in  the  area  of  initially  high 
recruitments,  site  effects  will  be 
reduced.  Another  way  to  approach  this 
problem  is  to  outplant  sporophytes  at 
differing  densities,  and  record  subsequent 
growth  and  survival. 

It  has  been  suggested  for  some 
species  in  the  Fucales  that  higher 
densities  of  adult  plants  result  in 
release  en  masse  of  gametes,  which  may  be 
important  for  good  recruitment  (Fletcher 
and  Fletcher  1975,  Schiel  1981).  Greater 
densities  may  also  be  important  to  effect 
successful  fertilization  of  gametophytes 
(that  is,  for  males  to  find  females). 
There  is  little  information  on  these  early 
life  stages  and  density  for  Macrocystis. 

Macrocystis  forests  may  be  extensive 
in  size,  with  relatively  high  densities  of 
plants  and  virtually  100%  cover  of  the  sea 
surface  by  algal  fronds.  Little  is  known 
about  the  importance  of  "patch  size"  to 
the  growth,  eventual  sizes  of  plants,  and 
reproduction.  Macrocystis  in  small 
patches,  such  as  artificial  reefs,  tend  to 
suffer  rapid  deterioration  and  mortality 
due  to  fish  grazing  (LOSL  1983).  The 
effects  and  importance  of  patch  size  can 
be  tested,  and  are  relevant  to  attempts  at 
establishing  algal  populations  where  they 
do  not  presently  occur. 

5.5.3  Spore  Dispersal 

General  Hypothesis:  The  distribution 
of  algal  spores  or  their  differential 
mortality  account  for  the  distribution  of 
adult  plants. 

The  problem  of  determining  whether 
spores  have  actually  arrived  to  an  area  is 
important  to  arguments  about  competition 
among  species  (Denley  and  Dayton  in 
press).  There  is  increasing  evidence  that 
spore  or  germling  dispersal  is  limited  for 
many  brown  algal  species,  with  most 
recruits  appearing  within  a  few  meters  of 
reproductive  adult  plants  (Anderson  and 
North  1966;  Dayton  1973;  Paine  1979; 
Schiel  1981,  in  press  b;  Deysher  and 
Norton  1982).  The  problem  of  whether 
algal  germlings  can  survive  and  grow  in 


zones  different  from  where  adult  plants 
normally  occur  has  been  addressed  in  a  few 

In  a  study  in  New  Zealand,  Schiel 
(1981)  settled  Sargassum  sinclairii 
germlings  onto  plates,  and  placed  them  on 
a  shallow  reef  (5  m)  where  adult  plants 
were  abundant  and  on  a  deep  reef  (15  m) 
where  adult  plants  were  scarce.  Initial 
survival  of  germlings  was  better  in  the 
deep  area.  Once  the  young  plants  began  to 
form  blades,  however,  shallow  plants  grew 
at  a  much  faster  rate,  while  most  deep 
plants  grew  slowly  and  eventually  died. 
Schiel  (1981)  speculated  that  the  major 
reason  for  few  adult  Sargassum  plants  in 
deep  areas  was  that  germlings  rarely 
reached  these  habitats  in  great  abundance, 
and  that  the  few  which  did  settle  had  a 
low  probability  of  growth  and  survival. 
As  in  the  studies  of  Schonbeck  and  Norton 
(1978,  1980)  and  Kennelly  (1983),  small 
Crustacea  were  probably  important  sources 
of  mortality  for  germlings  which  grew 

Adult  distribution  may  also  be  a 
reflection  of  spore  distribution.  This  is 
a  persistent  problem  in  algal  research, 
and  one  which  is  only  just  beginning  to  be 
addressed  (e.g.,  Kennelly  1983).  Spore 
fall  is  probably  not  evenly  distributed  in 
natural  situations,  and  may  be  affected  by 
current  and  surge  conditions  in  much  the 
same  way  as  "seed  shadows"  occur  in  some 
terrestrial  situations  (Harper  1977). 
Dense  aggregations  of  spores  or  germlings 
may  also  be  important  to  the  production  of 
large  algal  stands  (Fletcher  and  Fletcher 
1975,  Fletcher  1980).  Denley  and  Dayton 
(in  press)  suggest  ways  in  which  spore 
fall  may  be  examined  using  settlement 
plates  and  microscopic  examinations,  and 
techniques  are  now  available  for  j_n  situ 
microscopic  examination  of  substrata 
(Kennelly  and  Underwood  1984).  In  such  an 
experiment,  Chapman  (1984)  found  that  the 
greatest  proportional  mortality  for 
Laminaria  longicruris  and  Jl.  digitata 
occurred  between  the  time  the  microscopic 
plants  attached  to  the  substratum  and  when 
they  became  visible,  a  period  of  about  6 
weeks  (see  Section  for  a 
description  of  his  experiments).  This  is 
a  unique  study  in  that  it  assesses  the 
number  of  spores  produced  for  adult  plants 
per  square  meter,  the  recruitment  of 

microscopic  sporophytes  that  results  from 
these  spores,  the  visible  recruitment  of 
macroscopic  sporophytes  to  natural 
substrata  in  the  field,  and  the  subsequent 
survivorship  of  the  plants.  This  kind  of 
innovative  study  is  essential  to  clarify 
the  distribution  histories  of  species,  and 
to  assess  whether  competition  among  algal 
species  is  an  important  structuring  force 
in  algal  communities. 


General  Hypothesis:  The  activities 
of  grazers  affect  the  distribution  and 
abundance  of  large  brown  algae. 

Many  studies  mention  that  the 
activities  of  grazers  affect  the 
distribution  and  abundance  of  large  brown 
algae  in  subtidal  regions,  but  there  have 
been  relatively  few  experimental  studies 
which  assess  the  nature  of  their  effects. 
Most  of  our  present  knowledge  about  the 
effects  of  grazers  on  algal  assemblages 
comes  from  experimental  studies  in 
intertidal  areas,  where  herbivorous 
gastropods  are  usually  the  most  abundant 
and  important  grazers  (Underwood  1979,  for 
review).  Much  of  the  small-scale 
patchiness  in  the  abundances  of  intertidal 
algae  is  caused  by  grazing  on  filamentous 
and  foliose  plants,  as  well  as  on  algal 
spores  (e.g.,  Dayton  1971;  Underwood  and 
Jernakoff  1981,  1984).  Algal  cover  and 
diversity  may  be  dependent  on  the  density 
of  grazers  in  a  given  area  (Lubchenco 
1978,  Underwood  et  al.  1983). 

The  regime  of  grazing  generally 
changes  abruptly  in  the  boundary  between 
intertidal  and  subtidal  regions.  Even  on 
shores  where  the  abundances  of  herbivorous 
gastropods  such  as  limpets  and  trochids 
are  great,  their  distribution  tends  to  end 
where  the  zone  of  dense  algae  (normally 
fucoids)  begins  in  the  immediate  subtidal. 
Herbivorous  gastropods  tend  to  be  less 
abundant  in  the  subtidal  ,  where  sea 
urchins  are  normally  the  major  grazing 
invertebrate.  Herbivorous  fish  may  also 
affect  subtidal  algal  assemblages  (Choat 
1982,  Gaines  and  Lubchenco  1982). 


5.6.1  Invertebrate  Grazers  (Other  Than 
Sea  Urchins) 

There  are  few  published  experimental 
studies  that  have  assessed  the  effects  of 
gastropods  on  algae  in  subtidal  regions. 
A  recent  study  by  Watanabe  (1983,  1984a) 
in  central  California  assessed  some  of  the 
effects  of  three  species  of  Tegula  in  a 
shallow  Macrocystis  forest.  These  gas- 
tropods normally  live  and  feed  on  the 
fronds  and  laminae  of  Macrocystis.  During 
and  after  storms  they  are  abundant  on  sub- 
strata below  the  plants,  but  quickly 
occupy  fronds  again  when  calmer  conditions 
ensue.  Their  grazing  activities,  however, 
had  no  discernible  effect  on  algal  distri- 
bution or  abundance. 

Schiel  and  Foster  (unpublished  data) 
noted  an  increase  in  abundance  of  Tegula 
on  the  substratum  of  reefs  in  central 
California  after  winter  storms  removed  the 
fronds  of  most  Macrocystis  plants.  Tegula 
grazed  heavily  on  the  broken  ends  of  old 
fronds  and  also  on  younger  fronds, 
preventing  them  from  growing.  Tegula  also 
grazed  the  ends  of  blades  on  Pterygophora 
which  were  damaged  in  the  same  storms. 
These  effects  were  not  long-lasting, 
however,  as  the  vegetative  blades  and 
sporophylls  re-grew  in  the  spring. 

Schiel  (1981)  used  both  exclusion  and 
inclusion  cages  to  assess  the  effects  of 
limpets  and  turbinid  and  trochid  gastro- 
pods in  the  shallow  subtidal  of  northern 
New  Zealand.  Limpets  and  turbinids  could 
prevent  the  establishment  of  large  brown 
algae  on  a  small  scale  (25  x  25  cm 
patches),  presumably  by  grazing  algal 
spores.  These  grazers  had  greater  effects 
at  higher  densities. 

Other  invertebrate  grazers  such  as 
abalone  (Hal iotis  spp.)  and  sea  stars 
(Patiria  spp. )  may  have  small-scale 
effects  on  algal  abundances  in  Macrocystis 
forests,  but  their  effects  have  not  been 
assessed.  Small  Crustacea  can  be  very 
abundant  in  algal  turfs  (cf.  Kennelly 
1983)  and  may  be  major  grazers  on  algal 
spores.  Experiments  assessing  their 
effects,  and  the  interactions  of  grazers 
that  co-occur  on  areas  of  substratum,  have 
yet  to  be  done.  There  also  may  be 
indirect  effects  of  invertebrates  on  algal 
assemblages.   For  example,  Santelices  et 

al.  (1983)  have  shown  that  spores  of  many 
seaweeds  can  survive  digestion  by  sea 
urchins,  and  suggest  that  this  may  affect 
the  abundance  of  opportunistic  plants  in 
grazed  areas  and  perhaps  the  dispersal  of 
species  that  occur  later  in  succession. 
Schroeter  et  al .  (1983)  found  that  the  sea 
star  Patiria  was  an  abundant  predator  of 
Lytechinus  anamesus  in  the  San  Onofre  kelp 
forest,  affecting  the  local  distribution 
of  the  sea  urchin.  This  echinoid  can  be 
an  important  grazer  of  juvenile 
laminarians  in  local  patches  (Dean  et  al. 
1984),  and  an  alteration  in  its  dispersion 
patterns  could  allow  successful 
recruitment  of  kelps.  Tegner  and  Dayton 
(1981)  suggested  that  the  spiny  lobster, 
Panul irus  interruptus ,  may  be  a  major 
predator  of  sea  urchins  in  southern 
California.  This  again  could  have  effects 
on  algal  assemblages  by  reducing  the 
incidence  of  grazing.  Laboratory 
experiments  indicated  that  lobsters  would 
eat  echinoids,  but  no  data  were  presented 
on  lobster  abundances  in  the  kelp  forest, 
making  it  difficult  to  assess  their 
present  effects. 

5.6.2  Effects  of  Fish 

A  few  species  of  fish  in  Macrocystis 
forests  are  known  to  include  algae  in 
their  diets  (Quast  1968).  A  recent  study 
by  Harris  et  al.  (1984)  suggested  that 
fish,  particularly  the  halfmoon,  Medial  una 
cal iforniensis,  and  the  opal  eye,  Girella 
nigricans,  can  be  important  grazers  of 
small  Macrocystis  sporophytes  on  a  local 
scale.  At  Naples  Reef  off  Santa  Barbara, 
fishes  grazed  about  59%  of  sporophytes 
(<  10  cm  tall)  that  were  concealed  in  a 
turf  of  ephemeral  algae,  while  94%  of 
those  on  open  reef  quadrats  were  grazed. 
They  reported  that  plants  >  10  cm  in 
height  were  not  grazed,  suggesting  a  size 
refuge  from  fish  grazing.  The  result  of 
this  grazing  was  a  small-scale  change  in 
the  dispersion  pattern  of  juvenile 
Macrocystis  on  the  reef.  They  did  not 
report  the  abundances  of  the  fish  present 
over  the  reef,  however,  and  no 
observations  of  fish  feeding  behavior  were 

There  are  no  studies  that  demonstrate 
extensive  modification  of  the  biota  by 
grazing  fishes  in  Macrocystis  forests. 
Indirect  effects  are  reported  in  some 


studies.  Bernstein  and  Jung  (1979) 
recorded  that  Oxyjulis  cal ifornica  may 
feed  on  the  bryozoan,  Membranipora,  and 
mobile  invertebrates  that  inhabit  the 
laminae  of  Macrocystis.  They  suggested 
that  the  removal  of  these  invertebrates  by 
Oxyjul is  may  free  the  fronds  from 
extensive  encrustation  and  grazing. 

Other  anecdotal  information  (LOSL 
1983)  records  that  fish  had  a  severe 
grazing  effect  on  large  Macrocystis  plants 
that  were  moved  to  the  Pendleton 
Artificial  Reef,  off  San  Onofre.  Large 
numbers  of  halfmoon  and  opaleye  were 
attracted  to  these  reefs,  and  they  quickly 
moved  to  the  transplanted  Macrocystis 
plants  moored  on  the  reefs.  Predation  of 
invertebrates  and  grazing  of  frond  tissue 
by  these  fish  caused  the  demise  of 
Macrocystis  within  a  few  weeks. 

Other  indirect  effects  of  fish  on 
algal  assemblages  have  been  reported. 
Cowen  (1983)  found  in  the  San  Nicolas 
Island  kelp  forest  that  an  alteration  in 
the  abundance  of  the  sheephead  wrasse, 
Semicossyphus  pulcher,  could  affect  local 
populations  of  the  sea  urchin,  S^. 
f ranciscanus.  When  sheephead  were  removed 
from  a  site,  there  was  a  slight  increase 
in  the  number  of  sea  urchins.  He  also 
recorded  that  in  areas  where  sheephead 
densities  were  low,  echinoids  were  highly 
exposed,  whereas  in  areas  with  high 
densities  of  the  wrasse,  echinoids  tended 
to  be  concealed  in  crevices.  Nelson  and 
Vance  (1979)  and  Tegner  and  Dayton  (1981) 
also  reported  that  the  densities  of  sea 
urchins  may  be  altered  by  Semicossyphus. 
In  all  of  these  studies,  however,  the 
effects  of  sea  urchin  removal  on  the  algal 
assemblages  are  not  clear. 

It  would  be  useful  to  do  experiments 
that  assess  the  effects  of  fishes  on 
juvenile  algae  and  of  feeding  on  the 
substrata  where  algae  can  recruit. 
Exclusion  of  fishes  by  cages  and  shields 
have  been  successful  in  some 
circumstances.  Of  particular  interest  is 
the  variability  of  grazing  effects  and  the 
scales  at  which  they  occur.  Are  the 
effects  quite  localized  in  some  areas  of 
particular  reefs,  or  are  there  broader 
scale  effects?  A  necessary  part  of  such 
studies  is  a  record  of  the  abundances  of 
each  species  of  fish  in  experimental 

sites,  and  observations  of  their  feeding 
behavior  to  determine  how  selective 
feeding  is.  Choat  (1982)  gives  a  thorough 
review  of  the  effects  of  fish  feeding  on 
the  biota  of  temperate  shores. 

5.6.3  Sea  Urchins 

If  there  is  any  generalization  that 
has  made  its  way  to  prominence  in  the 
literature  dealing  with  kelp  communities, 
it  is  the  dominating  effect  of  sea  urchins 
on  the  distribution  and  abundance  of  large 
brown  algae.  The  words  "control"  and 
"regulating"  are  frequently  used  when 
discussing  the  effects  of  echinoids  on 
algae,  and  "overgrazing"  is  often 
mentioned,  evocative  of  an  untoward  shift 
from  a  "natural"  community  dominated  by 
large  macroalgae  (e.g.,  Estes  et  al.  1978, 
Kain  1979,  Duggins  1980,  Tegner  and  Dayton 
1981).  The  general  implication  has  been 
that  the  grazing  activities  of  sea  urchins 
have  a  comprehensive  effect  on  the 
character  of  the  biotic  assemblages  on 
rocky  reefs.  This  argument  has  also  been 
expanded  to  an  evolutionary  context, 
suggesting  that  the  evolution  of  kelp  life 
histories  and  competitive  abilities  may  be 
the  result  of  responses  to  echinoid 
grazing  activities  (Vadas  1977,  Steinberg 
1984,  Estes  and  Steinberg  MS.). 

There  is  little  argument  that  sea 
urchins  of  many  species  may  have  dramatic 
effects  on  kelp  assemblages  on  most 
temperate  shores  in  both  hemispheres 
(Lawrence  1975).  The  relatively  rapid 
denudation  of  algal  stands  by  mobile 
aggregations  of  sea  urchins  have  been  the 
focus  of  many  investigations  (e.g., 
Leighton  et  al.  1966,  North  1974,  Lawrence 
1975,  Dean  et  al.  1984).  It  is  also  clear 
that  kelp  can  be  abundant  and  persist  in 
close  proximity  to  echinoids  (Foster 
1975b,  Cowen  et  al.  1982,  Dean  et  al . 
1984,  Dayton  et  al.  1984,  Harrold  and  Reed 
in  press).  Largely  lacking,  however,  are 
detailed  distributional  data  which  examine 
the  various  spatial  and  temporal  scales  of 
echinoid  abundance.  Within  a  site,  for 
example,  the  abundance  of  sea  urchins  is 
not  constant,  and  may  change  with  depth 
(Mann  1972a,  Estes  et  al.  1978,  Kain  1979, 
Foster  1982a,  Choat  and  Schiel  1982). 
There  may  also  be  differences  in 
abundances  between  local  sites,  between 
areas  along  a  shoreline,  and  latitudinal 


differences  along  coastlines  occupied  by 
kelp.  A  better  knowledge  of  these 
distributional  scales  would  provide  a 
context  for  assessing  the  general 
importance  of  grazing  by  echinoids. 

Within  sites  where  sea  urchins  are 
abundant,  their  effects  have  been 
generally  documented  in  three  categories: 
(1)  wholesale  removal  of  algae;  (2)  the 
alteration  of  species  diversity  via 
feeding  preferences  and  selective  removal 
of  algal  species;  and  (3)  the  provision  of 
cleared  primary  substratum  suitable  for 
kelp  recruitment.  We  will  discuss  these 

It  is  commonly  observed  worldwide 
that  dense  aggregations  of  sea  urchins  may 
remove  large  tracts  of  algae,  creating 
so-called  "barren  grounds"  (see  Lawrence 
1975  for  review).  After  the  dense 
vanguard  of  sea  urchins  has  passed,  their 
densities  may  decline,  but  may  remain  high 
enough  to  prevent  successful  kelp 
recruitment  for  many  years  in  particular 
depth  strata  (Chapman  1981,  Andrew  and 
Choat  1982,  Breitburg  1984).  Thus,  large 
persistent  patches  without  kelp  may  occur 
in  areas  where  sea  urchins  are  abundant. 
These  areas  devoid  of  large  brown  algae 
often  support  a  high  cover  of  encrusting 
organisms  (Ayling  1981,  Choat  and  Schiel 
1982,  Breitburg  1984).  There  is  no 
conclusive  evidence  for  generalizations 
about  the  more  subtle  effects  of  grazers 
in  kelp  forests,  as  most  investigations 
have  focused  on  "barren"  areas.  Cowen  et 
al.  (1982)  suggested  that,  at  low 
densities,  sea  urchins  may  indirectly 
increase  bottom  cover  of  red  algae  by 
removing  overstory  brown  algae  that  shade 
the  bottom.  Results  of  intertidal  studies 
suggest  that  the  effects  of  grazing  on 
algal  cover  and  diversity  are  dependent 
upon  grazer  density  (Lubchenco  1978).  We 
can  find  no  published  account,  however,  of 
an  experiment  where  sea  urchin  densities 
were  artificially  increased  to  various 
levels  in  a  kelp  forest,  and  their 
subsequent  behavior,  movement,  and  feeding 
activities  recorded. 

Dean  et  al .  (1984)  used  a  series  of 
observations  and  experiments  to  assess  the 
effects  of  two  species  of  sea  urchins  on 
Macrocystis  in  the  San  Onofre  kelp  forest. 
Two  different  modes  of  feeding  were  seen 

for  S.  f  ranciscanus.  Over  3  years, 
aggregations  were  either  relatively  small 
and  stationary,  or  large  and  mobile, 
advancing  at  the  rate  of  2  m/month. 
Stationary  aggregations  fed  mainly  on 
drift  kelp  and  had  no  significant  effect 
on  kelp  recruitment  and  abundance.  Mobile 
aggregations  of  red  sea  urchins,  however, 
removed  most  macroalgae  in  their  path. 
Small  transplanted  Macrocystis  were 
consumed  over  a  2-day  period  in  the  mobile 
aggregation,  but  remained  intact  amongst 
stationary  echinoids  and  in  a  contral  area 
with  no  sea  urchins.  The  results  of  a 
similar  experiment  for  Lytechinus  anamesus 
were  equivocal,  with  small  Macrocystis 
being  consumed  in  some  trials  and  ignored 
in  others.  Of  particular  interest  in  this 
study,  however,  was  the  careful  3-year 
observations  of  kelp  and  echinoid 
abundances  along  several  transects  through 
the  kelp  forest.  Stationary  and  mobile 
aggregations  of  echinoids  occurred  within 
100  m  of  each  other,  and  feeding  fronts  of 
sea  urchins  were  seen  only  twice  during 
the  course  of  the  study.  These  quite 
different  modes  of  feeding  activity  were 
very  local-scale  events,  and  apparently 
were  dictated  by  the  unavailability  of 
drift  algae  leading  to  a  change  in  the 
foraging  behavior  of  the  sea  urchins. 
Dean  et  al.  (1984)  also  concluded  that 
both  types  of  aggregations  appeared  to  be 
unrelated  to  predation  pressure  from 
lobsters  and  fishes,  although  density 
estimates  for  these  predators  were 
anecdotal . 

Many  studies  have  shown  that  a 
preference  hierarchy  can  be  established 
for  sea  urchins  consuming  algal  species  in 
laboratory  experiments  (Leighton  1961, 
Lawrence  1975,  Vadas  1977).  A  major 
question  is  whether  these  preferences 
reflect  the  manner  in  which  algae  are 
removed  j_n  situ  by  the  same  sea  urchin 
species.  Vadas  (1977),  for  example,  found 
that  Strongylocentrotus  droebachiensis 
clearly  preferred  Nereocystis  1 uetkeana  to 
Agarum  cribosum  in  laboratory  experiments. 
Sea  urchins  grew  faster,  and  had  a  greater 
reproductive  output  when  fed  Nereocystis 
for  long  periods.  He  postulated  optimal 
feeding  strategies  for  sea  urchins  in 
nature,  and  argued  for  the  coevolution  of 
algae  and  urchins  based  on  selective 
removal,  plant  defenses  and  benefits  to 
urchins.   This  study,  however,  indicated 


that  sea  urchins  in  nature  fed  mainly  on 
drift  Nereocystis,  plants  which  had 
already  been  removed  by  other  causes.  In 
addition,  the  densities  of  urchin 
aggregations  were  not  mentioned  as  a 
factor  important  to  plant  removal.  Other 
studies  have  shown  that  sea  urchin 
densities  can  be  important  in  nature. 
Breen  and  Mann  (1976)  found  that  there  was 
a  non-linear  effect  of  sea  urchin  numbers 
on  algal  removal  in  Laminaria  longi cruris 
beds  in  Nova  Scotia.  Schiel  (1982)  also 
postulated  a  non-linear  effect  of  sea 
urchin  feeding  for  subtidal  areas  in 
northern  New  Zealand.  In  parallel 
laboratory  and  field  experiments,  he  found 
that  the  removal  of  plant  material 
increased  exponentially  with  sea  urchin 
numbers.  He  also  found  that  there  was  no 
correlation  between  the  feeding  preference 
hierarchies  found  in  the  laboratory,  and 
those  found  in  experimental  situations  in 
the  field.  The  order  of  removal  of  algal 
species  by  sea  urchins  from  natural  stands 
appeared  to  be  related  to  holdfast 
morphology,  and  was  not  correlated  with 
hierarchies  established  in  field 
experiments.  Because  sea  urchins  clumped 
on  some  replicates,  and  their  feeding 
effect  was  non-linear,  Schiel  (1982) 
postulated  an  "all-or-nothing"  effect  of 
sea  urchins  on  kelp  removal. 

A  contrasting  result  was  found  by 
Harrold  and  Reed  (in  press)  at  San  Nicolas 
Island.  Red  sea  urchins  (Strongylocentro- 
tus  franciscanus)  were  abundant  both  in 
Macro_£y_sti_s -dominated  areas  and  in  patches 
devoid  of  large  brown  algae.  The  movement 
of  the  echinoids  and  their  effects  on  the 
epibenthic  community  were  affected  by  the 
availability  of  drift  Macrocystis.  Red 
sea  urchins  moved  greater  distances  and 
fed  on  benthic  organisms  in  "barren" 
patches,  while  they  remained  relatively 
stationary  and  fed  on  drift  kelp  in 
Macrocystis  patches.  This  result  is 
similar  to  that  found  by  Mattison  et  al. 
(1977)  in  central  California.  One  of  the 
major  differences  between  the  activities 
of  echinoid  grazers  in  the  eastern  Pacific 
and  those  elsewhere  may  therefore  be 
related  to  the  preponderance  of  large 
kelps,  and  hence  ample  drift  material, 
compared  to  the  smaller  stipitate 
laminarians  found  in  most  other  parts  of 
the  world. 

Much  time  and  money  have  been,  and 
are  being,  spent  on  "the  urchin  problem" 
(North  and  Pearse  1970,  North  1983a)  in 
southern  California.  The  "problem" 
appears  to  arise  primarily  from  a 
management  viewpoint  that  Macrocystis 
forests  are  desirable,  are  the  unvarying 
natural  state  of  coastal  waters,  and  the 
perception  that  localized  aggregations  of 
kelp-destroying  sea  urchins  are  somehow 
man-induced  (Bascom  1983).  Although  this 
may  be  the  case  near  large  sewage 
outfalls,  it  is  equally  likely  that  waste 
discharge  caused  a  reduction  in  algal 
biomass,  and  the  urchins  are  simply  eating 
what  is  left  (see  Chapter  6).  Moreover, 
recent  observations  suggest  that  urchin 
"barren"  grounds  may  come  and  go  in  kelp 
forests  as  natural  variations  in  a  dynamic 
community  (see  Chapters  3  and  4). 
Nevertheless,  the  consequent  assaults  on 
the  lowly  and  meddlesome  sea  urchins  have 
taken  epic  proportions,  from  destruction 
of  tests  with  quicklime  to  outright 
mechanical  maceration  (Chapter  6).  There 
was  also  a  major  effort  organized  through 
SCUBA  diving  clubs  to  smash  sea  urchins 
with  hammers  (North  1972a).  These 
projects  have  met  with  only  limited 
success.  In  some  cases,  Macrocystis 
became  locally  established,  while  in 
others,  fish  grazing  and  probably 
limitations  in  algal  spore  dispersal 
prevented  establishment  (North  1972a, 

Evidence  from  studies  elsewhere 
indicates  that  when  adult  plants  are 
nearby,  the  removal  of  sea  urchins  can 
result  in  a  large  recruitment  of  kelp 
(Jones  and  Kain  1967,  Duggins  1980,  Andrew 
and  Choat  1982).  An  experimental  study 
examining  this  for  Macrocystis  forests  was 
done  by  Pearse  and  Hines  (1979)  near  Santa 
Cruz,  central  California.  Large  numbers 
of  Strongylocentrotus  franciscanus  died 
over  a  wide  area  along  the  edge  of  a  large 
stand  of  Macrocystis  as  a  result  of 
disease  (see  Section  4.7).  Dense 
recruitment  of  Macrocystis,  Pterygophora 
cal ifornica,  and  Laminaria  dentigera 
occurred  during  the  following  spring  in 
the  previously  urchin-dominated  area.  The 
boundary  of  the  kelp  forest  also  was 
extended  seaward  by  over  100  m  due  to  the 
removal  of  echinoids  and  their  legacy  of 
cleared  substratum. 


As  with  previously  discussed  aspects 
of  experimental  work  in  algal  forests,  the 
interactions  of  physical  and  biological 
factors  are  important  determinants  of 
spatial  and  temporal  heterogeneity  within 
a  depth  stratum,  yet  studies  have 
previously  been  constrained  to  looking  at 
only  main  effects.  Large  physical 
disturbances  such  as  severe  winter  storms 
can  differentially  affect  kelp  species 
with  long-term  consequences  for  community 
composition  (Dayton  and  Tegner  1984b, 
Ebeling  et  al.  MS.,  Schiel  and  Foster  in 
prep.).  There  are  many  important  factors 
which  have  not  been  tested,  and  which 
could  be  important  in  many  of  the  studies 
mentioned  in  this  chapter  (see  Figure  24). 
For  example,  the  abundance  of  echinoids 
and  grazing  gastropods  can  be  positively 
correlated  (Ayling  1981,  Simenstad  et  al. 
1978)  and  may  be  synergistic  in  some  of 
their  grazing  activities.  Alteration  of 
kelp  canopies  and  the  abundances  of 
fleshy,  encrusting  or  articulated  red 
algae  not  only  alters  the  available  space 
and  the  irradiance  levels,  but  also  the 
local  grazing  regimes,  particularly  small 
echinoids  and  herbivorous  micro- 
invertebrates.  The  size  of  kelp  stands 
could  also  be  important  in  determining 
community  structure  (c.f.,  Dayton  and 
Tegner  1984a),  although  there  is  little 
experimental  evidence  for  this.  Suitably 
designed  field  experiments  testing 
specific  hypotheses  offer  a  promising 
approach  to  addressing  these  problems  and 
removing  the  answers  from  the  equivocal 
realm  of  anecdote,  conjecture,  and 


importance  of  sea  otter-sea  urchin-kelp 
relationships  is  based  on  three  types  of 
evidence:  (1)  When  large  numbers  of  sea 
urchins  are  present  in  an  area,  kelp 
abundance  may  be  low  (see  references  in 
previous  section).  (2)  Sea  otters 
preferentially  feed  on  large  sea  urchins 
when  urchins  are  available.  In  areas 
where  otters  are  abundant,  sea  urchins 
tend  to  be  scarce  and  small  in  size  (Estes 
et  al.  1978,  Breen  et  al.  1982,  Van 
Blaricom  in  press).  (3)  Historical 
evidence  indicates  that  sea  otters  were 
once  abundant  along  the  west  coast  of 
North  America  and  were  important  predators 
in  kelp  forests  (Estes  and  Van  Blaricom  in 
press) . 

Estes  et  al.  (1978)  examined  the 
distribution  and  abundances  of  kelp  and 
sea  urchins  at  different  sites  in  the 
Bering  Sea,  some  of  which  had  populations 
of  sea  otters.  Strongylocentrotus 
polyacanthus  were  particularly  abundant 
only  in  the  site  without  otters,  where 
there  was  little  macroalgae.  Sea  urchins 
were  larger  at  this  site  when  compared  to 
the  site  where  otters  actively  foraged. 
Estes  et  al.  (1981)  found  that  in  recently 
repopulated  areas  of  the  Aleutian  Islands, 
sea  otter  diets  consisted  mainly  of  sea 
urchins,  whereas  epibenthic  fish  were  the 
most  important  prey  to  an  established 
otter  population.  Duggins  (1980)  provided 
experimental  information  from  Alaska 
showing  that  when  dense  aggregations  of 
echinoids  are  removed,  a  lush  algal  flora 
may  develop.  At  the  sites  examined  in 
Alaska,  the  evidence  is  that  otters  may  be 
a  "keystone  species"  (c.f.  Paine  1966, 
Estes  et  al.  1978)  in  shallow  communities. 

General   Hypothesis: 
enhance  kelp  abundance  by 
urchins,  the  major  grazers. 

Sea   otters 
removing  sea 

As  already  discussed  in  Section,  sea  otters  (Enhydra  lutris) 
consume  up  to  a  fourth  of  their  body 
weight  in  food  per  day,  feeding  on  a  wide 
range  of  invertebrate  species.  Attempts 
at  experimentally  assessing  their  effects 
on  nearshore  communities  have  been 
hampered  by  the  obvious  logistic 
constraints  of  dealing  with  a  mobile 
predator  and  the  use  of  "natural 
experiments,"  that  is,  comparing  areas 
with   and   without   sea   otters.    The 

The  evidence  is  not  so  clear  for  the 
population  of  sea  otters  in  California. 
Van  Blaricom  (in  press)  reviewed  the 
literature  concerning  the  recent  expansion 
of  the  range  of  sea  otters  along  the 
central  coast  of  California.  Dense  sea 
urchin  populations  were  reduced  along  the 
Monterey  Peninsula,  leaving  generally 
small,  concealed  individuals  (McLean  1962, 
Lowry  and  Pearse  1973).  Indeed,  there  are 
no  examples  of  dense  aggregations  of  sea 
urchins  persisting  where  otters  are 
present.  Van  Blaricom  noted  that 
Nereocystis,  an  annual  plant,  tends  to 
persist  in  the  presence  of  sea  urchins 
while  Macrocystis  does  not.   From  recent 


canopy  maps,  he  postulated  a  change  from 
Nereoystis  to  Macrocystis  after  otters 
removed  sea  urchins.  While  this  may  be 
the  case  for  some  sites  in  central 
California,  the  evidence  is  equivocal  for 
others.  Sea  urchins  are  quite  patchy  in 
their  distribution  and  effects,  and  there 
is  often  not  a  straightforward 
relationship  between  their  abundances  and 
that  of  particular  kelp  species  (see 
references  in  previous  section).  In 
addition,  winter  storms  and  turbulent  sea 
conditions  can  affect  kelp  abundance; 
Nereocystis  tends  to  replace  Macrocystis 
in  such  cases  (e.g.,  Cowen  et  al .  1982) . 
To  resolve  these  questions,  a  better 
understanding  is  needed  of  the  effects  of 
sea  urchins  in  kelp  forests  without 
otters.  Macrocystis  communities  can 
certainly  exist  in  the  presence  of  this 
grazer.  Giant  kelp  communities  are 
vaiable  in  space  and  time,  however,  and 
dense  aggregations  of  sea  urchins  may  be 
the  exception  rather  than  the  rule. 

The  historical  evidence  for  the 
effects  of  sea  otters  is  also  somewhat 
equivocal.  Simenstad  et  al.  (1978) 
examined  evidence  from  Aleut  middens  in 
Alaska  and  concluded  that  alternate  stable 
states  existed  in  nearshore  communities. 
They  argued  that  the  strata  containing 
large  quantities  of  sea  urchin  and  limpet 
shells  coincided  with  the  absence  of 

otters,  due  to  hunting  by  Aleuts.  The 

presence  of  fish  remains  coincided  with 

times  when  otters  were  present,  and 
macroalgae  predominated. 

There  is  also  evidence  in  the  middens 
in  Monterey  (Gordon  1974)  and  on  San 
Nicolas  Island,  off  southern  California, 
that  prehistoric  man  hunted  sea  otters. 
Dayton  and  Tegner  (1984a)  pointed  out  the 
large  numbers  of  abalone  shells  seen  on 
the  island,  suggesting  that  aboriginal  man 
had  a  significant  impact  on  the  nearshore 

Estes  and  Van  Blaricom  (in  press) 
reviewed  the  data  on  the  fluctuations  in 
many  shellfish  populations  and  the 
possible  effects  of  sea  otters.  The 
advent  of  otters  and  the  decline  of  many 
shell  fisheries  are  often  coincident  with 
increased  fishing  pressure,  pointing  to 
competition  between  modern  man  and  otters 
for  particular  resources.  They  concluded 
that  the  near  extinction  of  the  sea  otter 
permitted  the  development  of  shell 
fisheries  in  the  first  place.  While  these 
questions  are  interesting  and  relevant, 
the  interactions  between  otters, 
particular  fisheries,  and  natural 
variability  of  populations  are  complex  and 
have  forced  the  issues  more  into  the 
political  province  than  an  experimental 




Yet,  if  in  any  country  a  forest  was  destroyed,  I  do  not  believe 
nearly  so  many  species  of  animals  would  perish  as  would  here 
from  the  destruction  of  the  kelp.  Darwin  (1860). 


Giant  kelp  forests  are  an  important 
economic  and  recreational  resource.  North 
and  Hubbs  (1968)  estimated  the  value  of 
marine  resources  taken  from  kelp  forests 
near  La  Jolla  in  1955-56  at  nearly  a 
million  dollars.  In  current  dollars  and 
including  the  related  values  of  boats, 
diving  equipment,  tourism,  etc.,  this 
dollar  value  is  certainly  much  higher  (see 
also  estimates  in  North  1971b).  Moreover, 
living  near  the  ocean  is  desirable,  and 
disposing  of  wastes  in  nearshore  areas  is 
both  convenient  and  inexpensive  relative 
to  land  disposal  or  recycling.  Kelp 
forests  are  thus  heavily  used,  some  uses 
are  in  conflict  with  others,  and 
management  is  required  to  prevent 
deterioration.  This  is  particularly  true 
in  highly  populated  southern  California. 

The  preceding  chapters  have  reviewed 
the  diversity  and  dynamics  of  the  giant 
kelp  forest  community,  and  it  should  be 
clear  that  various  biotic  and  abiotic 
factors  may  interact  to  structure  the 
community  at  a  particular  site.  It  should 
also  be  clear  that,  for  most  of  these 
factors  and  interactions,  we  know  only 
what  is  plausible,  and  are  far  from  making 
quantitative  predictions  about  community 
dynamics  and  the  effects  of  particular 
perturbations.  In  this  context, 
management  is  presently  an  illusion. 
Predicting  the  effects  of  all  but  very 
extreme  changes  in  the  abiotic  environment 
or   in   particular   species   is   nearly 

impossible.  However,  man  continues  to 
harvest  organisms  from,  and  discharge 
wastes  into,  kelp  forests,  adding  to  the 
dynamics  of  the  system.  Moreover,  many  of 
the  groups  involved  in  these  activities 
are  politically  and/or  economically 
powerful,  making  management  decisions  even 
more  difficult  and  partly  removed  from  the 
meager  environmental  data  that  are 

Management  is  further  complicated 
because,  except  for  surface  canopies, 
observations  of  community  and  population 
changes  must  be  made  while  under  water. 
Even  occasional  surveys  in  a  few  forests 
require  trained  divers  and  considerable 
equipment.  In  addition  (and  for  the  same 
reasons),  background  information  against 
which  to  measure  change  is  lacking,  and 
there  may  be  multiple  factors  causing 
change  at  a  particular  site  (e.g., 
fishing,  sediment  from  river  discharge, 
waste  discharge)  or  in  a  particular  region 
(e.g.,  cumulative  waste  discharge  in 
southern  California,  changing  oceano- 
graphic  conditions).  Fay  et  al .  (1972) 
review  these  multiple  pollution  problems 
in  southern  California. 

Management  of  biotic  resources  has 
been  largely  by  regulation  based  on  catch 
statistics  for  particular  species.  The 
State  of  California  Department  of  Fish  and 
Game  has  primary  responsibility  for  most 
biotic  resources,  and  can  regulate  numbers 
of  fishermen,  catch  size,  and  areas 
fished.  The  Department  of  Fish  and  Game 
also  maintains  a  marine  mammal  research 


program,  and  recommends  management  policy, 
but  the  Marine  Mammal  Protection  Act  of 
1972  transferred  primary  responsibility 
for  sea  otters  to  the  United  States  Fish 
and  Wildlife  Service,  and  responsibility 
for  other  mammals  to  the  National  Marine 
Fisheries  Service. 

The  management  of  the  abiotic 
environment  of  kelp  forests  improved  con- 
siderably with  the  passage  of  the  federal 
Clean  Water  Act.  Prior  management  dealt 
almost  solely  with  questions  of  direct 
effects  on  human  health.  Many  agencies 
now  scrutinize  ocean  discharge  and 
construction  activities  that  may  alter 
nearshore  waters,  and  most  of  these  agen- 
cies require  the  maintenance  of  community 
"health"  and  "balance  of  indigenous  popu- 
lations." At  the  Federal  level,  these 
agencies  include  the  Environmental  Protec- 
tion Agency,  the  U.S.  Army  Corps  of 
Engineers  and  the  U.S.  Coast  Guard.  At 
the  State  level,  the  California  State 
Water  Resources  Control  Board  and  regional 
boards  regulate  discharge  into  the  ocean 
under  guidelines  set  forth  in  the 
California  Ocean  Plan.  Additional  control 
over  coastal  development  that  might  affect 
kelp  forests  is  provided  by  the  California 
Coastal  Commission  and  cities  and  counties 
through  local  coastal  programs. 


groups  for  abalone  food  (see  Animals 
below).  The  emphasis  has  shifted  from 
potash  to  algin  production.  Algin  is  a 
hydrocolloid  extracted  from  kelp  that, 
after  further  chemical  processing,  has  a 
variety  of  uses  as  an  emulsifying  and 
binding  agent  in  food  and  pharmaceutical 
industries  (Chapman  1970,  Frey  1971).  A 
number  of  regulations  have  been  imposed  by 
the  State  of  California  to  ensure  that 
harvesting  activities  have  a  minimal 
impact  on  kelp  forests  (see  Bowden  1981 
for  a  thorough  discussion).  Stands  of 
kelp  are  given  numbers  by  the  State,  and 
some  are  leased  to  harvesting  companies 
while  others  remain  open  to  anyone  with  a 
harvesting  permit.  These  companies  pay  a 
royalty  to  the  state  for  each  wet  ton  of 
kelp  harvested  (Bowden  1981).  Harvesting 
is  now  done  by  ships  with  large  cutting 
devices  on  the  stern  (Figure  30).  The 
ships  back  through  the  forest  and,  much 
like  a  hedge  trimmer,  cut  the  canopy  no 
lower  than  1.2  m  below  the  surface  in  a 
strip  8  m  wide.   This  allows  vegetative 


6.2.1  Plants  Macrocystis.  One  of  the 
oldest  and  economically  most  important 
uses  of  giant  kelp  forests  is  for  kelp 
harvesting.  Kelp  has  been  harvested  in 
California  since  1910  by  various  compa- 
nies. Nearly  400,000  wet  tons  per  year 
were  harvested  during  1917  and  1918 
(Oliphant  1979),  primarily  as  a  source  of 
potash  for  making  gunpowder  during  World 
War  I  (Hult  1917,  Frey  1971).  During  this 
period,  harvesting  was  often  done  by 
putting  a  cable  around  a  stand  of  kelp, 
and  dragging  the  plants  from  the  bottom 
with  little  regard  for  the  environment 
(McPeak  and  Glantz  1984). 

The  uses  of  kelp  and  the  methods  of 
harvest  have  changed  considerably  since 
the  early  1900' s.  At  present,  Kelco 
Company  in  San  Diego  is  the  major  harvest- 
er, with  small  amounts  taken  by  other 

Entire  ship 

i  n  w 

Kelp-harvesting  machinery  on  the  stern 

Figure  30.   A  modern  kelp-harvesting  ship 
operated  by  Kelco. 


regrowth  from  unharvested  subsurface 
fronds  on  cut  plants.  In  areas  where 
Nereocystis  "luetkeana  and  Macrocystis 
co-occur,  the  amount  of  _N.  luetkeana 
harvested  is  restricted  by  law.  Nereocys- 
tis luetkeana  is  an  annual,  and  its 
reproductive  blades  occur  near  the 
surface.  Harvesting  too  much  Nereocystis 
could  inhibit  its  re-establishment. 

Between  100,000  and  170,000  wet  tons 
of  Macrocystis  &re  currently  harvested 
annually  in  California  (Frey  1971, 
Oliphant  1979),  and  sales  by  the  kelp 
harvesting  industry  exceed  $35  million  a 
year  (Wilson  and  McPeak  1983).  Forests 
are  also  harvested  in  Mexico  with  plants 
imported  to  Kelco  Company  in  San  Diego. 
The  majority  of  the  California  harvest 
normally  comes  from  the  large  forests  in 
southern  California  (Barilotti  pers. 
comm.),  but  harvesting  occurs  as  far  north 
as  Carmel  Bay  in  central  California. 
Particular  stands  in  southern  California 
may  be  harvested  up  to  three  times  per 
year  (see  McPeak  and  Glantz  1984  for  a 
review  of  kelp  harvesting  and  uses). 

Kelp  harvesting  has  a  variety  of 
possible  impacts  on  giant  kelp,  kelp 
forests,  and  associated  nearshore 
communities.  Concern  over  these  impacts 
has  been  a  major  stimulus  for  kelp  forest 
studies  since  the  late  1950's.  The 
primary  concerns  have  been  the  possible 
destruction  of  kelp  stands,  destruction  of 
canopy-dwelling  invertebrates  and  fishes 
during  harvesting  operations,  reduction  in 
fish  populations  due  to  loss  of  food 
and/or  habitat,  and  an  increase  in  beach 
erosion  and  amount  of  drift  kelp  on 
beaches.  Early  studies  of  these  potential 
problems  were  summarized  by  North  and 
Hubbs  (1968),  who  concluded  that  "No 
adverse  influence  of  harvesting  could  be 
found  among  the  statistics  or  field 
observations  for  the  periods  studied." 
Uncut  fronds  grow  to  replace  those  cut, 
and  it  appears  that  only  occasionally  is 
an  entire  plant  torn  from  the  bottom 
during  harvesting  operations  (Rosenthal  et 
al .  1974).  Harvesting  the  canopy 
increases  light  on  the  bottom,  and  may 
enhance  recruitment  of  Macrocystis 
(Rosenthal  et  al.  1974,  Kimura  and  Foster 
in  press).  Miller  and  Geibel  (1973)  found 
that  adult  Macrocystis  abundance  declined 
after  repeated  experimental  canopy  removal 

at  Point  Cabrillo  near  Monterey.  Kimura 
and  Foster  (in  press)  found  no  adverse 
affects  after  a  single  experimental  har- 
vest in  Carmel  Bay.  The  latter  study  more 
closely  resembled  commercial  harvesting  as 
currently  practiced  in  Carmel  Bay,  and 
suggests  that  Miller  and  Geibel  's  (1973) 
results  represent  what  may  happen  in 
central  California  if  an  area  is  over- 
harvested.  Kimura  and  Foster  (in  press) 
did  find  that  the  timing  of  recruitment  in 
kelps  (Macrocystis  and  Pterygophora 
cal ifornica)  changed  in  harvested  areas, 
but  this  change  had  no  apparent  negative 
effects.  Barilotti  et  al.  (in  press) 
found  that  survivorship  of  adults  was  not 
reduced  in  the  two  harvested  forests  they 

No  overall  reduction  in  fishes  or 
invertebrates  in  particular  forests  has 
been  reported  due  to  harvesting  opera- 
tions, even  though  numerous  organisms  are 
removed  along  with  the  cut  fronds  (North 
and  Hubbs  1968,  Miller  and  Geibel  1973). 
Hunt  (1977)  did  find  significant  declines 
in  turban  snail  (Tegula  montereyi)  densi- 
ties in  harvested  areas  in  Carmel  Bay. 
Sea  otters  avoid  kelp  harvesting  ships, 
and  no  mortality  related  to  kelp  harvest- 
ing operations  has  been  reported  for  this 
or  other  mammals. 

Clendenning  (1971b)  estimated  that 
10%  or  less  of  Macrocystis  production  is 
removed  by  harvesters  in  harvested  for- 
ests. Possible  changes  in  consumer  popu- 
lations in  kelp  forests  or  elsewhere 
(beach,  offshore)  that  may  be  an  indirect 
result  of  removing  this  primary  production 
have  not  been  investigated. 

Recent  research  on  growing  Macro- 
cystis for  fuel  is  discussed  in  Section 
6.6.2.  Macrocystis  has  also  recently  been 
introduced  in  the  People's  Republic  of 
China  to  possibly  replace  Laminaria  as  a 
source  of  food  and  algin  (Foster  pers. 
obs.).  Other  plants.  The  only 
other  plant  commercially  harvested  from 
California  kelp  forests  is  Gel idium 
robustum,  a  source  of  high-quality  agar 
(Figure  17).  This  plant  is  occasionally 
harvested  by  divers  when  prices  are  high 
(Frey  1971).  The  plant  is  very  suscep- 
tible to  overharvesting,  as  it  grows 


slowly  and  does  not  appear  to  recruit 
rapidly  when  completely  removed  from  local 
areas  (Barilotti  and  Silverthorne  1972). 
One  company  has  recently  leased  a  near- 
shore  area  for  the  purpose  of  cultivating 
G.  robustum  (Bowden  1981). 

6.2.2  Animal s  Fishes.  North  (1971b)  lists 
37  species  of  fish  (including  "rockfish" 
as  one  species)  associated  with  kelp 
forests  that  occur  in  the  commercial  and 
party  boat  catch  in  California.  Most  of 
these  species  are  also  caught  in  areas 
without  kelp  forests,  and  catch  statistics 
are  not  reported  specifically  for  kelp 
communities.  Thus,  the  catch  and  status 
of  stocks  in  kelp  forests  are  uncertain. 
North  (1971b),  using  data  from  Davies 
(1968)  estimated  that  about  90%  of  the 
"rockbass"  (kelp  bass  plus  sand  bass) 
catch  for  southern  California  came  from 
areas  that  included  kelp  forests,  and  that 
about  70%  of  the  entire  party  boat  fish 
catch  came  from  areas  with  kelp. 

Drift  kelp  is  probably  an  important 
source  of  energy  for  communities  other 
than  kelp  forests,  so  kelp  forests  may 
indirectly  provide  some  of  the  energy  base 
for  fisheries  in  other  habitats  (see 
Chapters  3  and  4).  Moreover,  declines  in 
kelp  production  could  ultimately  be  re- 
flected in  declines  in  nearshore  fish 
stocks,  as  has  been  suggested  by  studies 
in  Alaska  (Estes  et  al .  1978). 

Miller  and  Geibel  (1973)  and  Love 
(1980)  indicated  that  some  fishes  may 
occur  in  local  populations  on  particular 
reefs,  with  little  movement  between  reefs. 
Thus,  local  areas  may  be  subject  to 
overfishing.  Miller  and  Geibel  (1973) 
recommended  management  by  zonal  opening 
and  closing  in  central  California. 

Tegner  (1980)  suggested  that  sheep- 
head  have  declined  due  to  overfishing  in 
some  southern  California  kelp  forests,  and 
because  these  fishes  eat  sea  urchins,  the 
declines  may  be  partly  responsible  for 
locally  high  urchin  densities.  Cowen's 
(1983)  experimental  sheephead  removal 
supports  this  latter  suggestion. 

Frey  (1971)  discussed  the  status  of 
other   California   fisheries,   including 

algae  and  invertebrates,  and  makes  a 
number  of  management  recommendations.  The 
catch  of  many  species  associated  with  kelp 
forests  is  declining,  and  it  is  commonly 
observed  that  large  individuals  have 
become  rare.  This  is  particularly  true  of 
Stereolepis  gigas,  the  giant  sea  bass,  in 
southern  California.  This  fish  is  occa- 
sionally found  in  giant  kelp  forests,  and 
is  listed  as  a  megacarnivore  by  Quast 
(1971a).  Large  individuals  (over  150  kg 
in  weight  and  2  m  long)  were  once  fairly 
common  and  must  have  been  an  impressive 
sight  swimming  through  the  kelp.  Unfor- 
tunately, recent  divers  have  been  denied 
this  experience  as  spear  and  hook-and-line 
fishermen  preyed  heavily  on  these  huge 
(and  perhaps  over  90  years  old;  Frey  1971) 
fish,  and  we  could  find  no  recent  observa- 
tions of  such  fish  in  kelp  forests.  Abalone.  Abalone  are  the 
only  commerically  fished  mollusc  in  Cali- 
fornia kelp  forests.  Animals  are  har- 
vested by  divers,  and  until  recently,  the 
main  species  taken  were  red  abalone  (Hal i- 
otis  rufescens)  and  pink  abalone  (H.  cor- 
rugata;  see  Section  In  the  peak 
year  of  1957,  slightly  over  five  million 
pounds  were  landed  (Cox  1962),  which  is 
roughly  a  million  and  a  half  animals 
(using  an  average  conversion  value  of  1 
doz.  abalone  =  40  lb.;  see  Cox  1962). 
Total  landings  have  declined  by  'v  80% 
since  1966  (Table  12),  due  to  overfishing 
(Tegner  1980),  habitat  loss,  illegal 
fishing,  improper  catch  methods  (Hardy  et 
al.  1982),  and  removal  by  sea  otters 
(Miller  and  Geibel  1973,  Hardy  et  al. 
1982).  However,  even  though  sea  otter 
foraging  was  highly  correlated  with  the 
decline  in  abalone  stocks  in  the  San  Luis 
Obispo  area  (Miller  and  Geibel  1973,  Hardy 
et  al.  1982),  this  area  contributed  only 
about  20%  of  the  total  California  catch  in 
1968  (calculated  from  data  in  Heimann  and 
Carlisle  1970).  Otter  foraging  in  the  San 
Luis  Obispo  area  began  around  1970  (Hardy 
et  al.  1982).  Thus,  factors  other  than 
sea  otter  foraging  have  had  a  great  impact 
on  the  statewide  decline  in  the  abalone 
fishery  noted  above  (see  also  Estes  and 
Van  Blaricom  in  press).  The  less  pre- 
ferred, shallow-water  black  abalone  (_H. 
cracherodii )  now  makes  up  the  majority  of 
the  catch  (Table  12). 


Table   12.     Commercial    landings  of  abalone,  lobsters,  and  sea  urchins   in 
California,    in   pounds. 







































Sea  Urchins 







From  Anonymous  1958. 

From  Heimann  et  al.  1968. 
:From  Oliphant  1979. 

Ebert  pers.  comm. 
'From  Cox  1962. 

The  mainland  coast  in  Los  Angeles  and 
Orange  Counties  has  recently  been  closed 
to  abalone  fishing  (Ebert  pers.  comm.), 
and  restoration  of  stocks  is  being 
attempted  by  planting  laboratory-grown 
juveniles  in  the  field.  These  restoration 
attempts  have  not  been  very  successful  , 
but  new  techniques  are  being  investigated 
(Ebert  pers.  comm.).  Even  if  restoration 
resulted  in  commercially  harvestable 
stocks  under  present  environmental  condi- 
tions, restoration  efforts  have  a  dim 
future  if  the  sea  otter  population  expands 
into  southern  California.  Sea  otters  can 
reduce  abalone  distribution  to  cracks  and 
crevices  where  individuals  are  barely 
accessible  to  man  (Lowry  and  Pearse  1973).  Sea  urchins.  Significant 
commercial  harvesting  of  red  sea  urchins 

(Strongylocentrotus  franc iscanus)  began  in 
1970  (tegner  and  Dayton  1977).  Animals 
are  harvested  by  divers,  and  the  roe  is 
extracted  and  shipped  mainly  to  Japan, 
where  it  is  considered  a  delicacy.  The 
California  sea  urchin  fishery  has  since 
expanded  rapidly  to  become  one  of  the 
largest  fisheries  in  the  State,  with  over 
17  million  pounds  landed  in  1982  (Table 

12).  Juvenile  red  sea  urchins  frequently 
occur  under  the  spines  of  adults  in  south- 
ern California  (Tegner  and  Dayton  1977). 
Thus,  removal  of  adults  not  only  reduces 
reproductive  potential,  but  also  affects 
juvenile  habitat,  so  the  potential  for  a 
high,  sustained  yield  from  the  fishery  may 
be  poor  (Tegner  and  Dayton  1977).  Wilson 
and  McPeak  (1983)  suggested  that  harvest- 
ing red  sea  urchins  may  result  in 
increased  abundances  of  purple  and  white 
sea  urchins.   Lobster.   The  spiny  lobster 

Panul irus  interruptus  is  commercially 
fished  with  traps  in  southern  California. 
Lobsters  are  often  associated  with  giant 
kelp  forests,  and  traps  are  frequently  set 
along  the  outer  and  inner  margins  of  the 
surface  canopies.  This  fishery  has  also 
declined  since  the  peak  harvests  of  the 
1950' s  (Tegner  1980;  Table  12),  and 
because  this  animal  can  eat  sea  urchins 
(Tegner  and  Dayton  1981,  Tegner  and  Levin 
1983),  Tegner  (1980)  suggested  that  local 
lobster  declines,  like  those  of  sheephead, 
may  be  partly  responsible  for  increased 
sea  urchin  abundance.  A  similar  scenario 
leading  to  extensive  losses  of  kelp  beds 


in  Nova  Scotia  was  proposed  by  Mann  and 
his  co-workers  (Mann  1973,  Breen  and  Mann 
1976;  but  see  Pringle  et  al.  [1980]  for 
alternative  views). 

Kelp  forests  are  also  a  source  of 
organisms  for  commercial  collectors  who 
sell  plants  and  animals  for  educational 
and  research  use.  The  number  of  organisms 
removed  is  probably  insignificant  relative 
to  commercial  and  sport  fisheries,  and 
most  are  otherwise  not  harvested  for  food 
by  anyone. 

6.2.3  Habitat  Use 

Commercial  and  recreational  boat 
traffic  often  goes  through  giant  kelp 
forests,  and  gaps  or  channels  through 
canopies,  created  by  propellers  cutting 
surface  fronds,  are  common  where  traffic 
is  heavy.  Occasional  small  strips  are  cut 
by  light  boat  traffic.  Heavy  traffic  may 
cause  a  reduction  in  adult  giant  kelp 
density,  and  an  increase  in  juvenile  kelp 
and  understory  red  algae  (North  1957). 
Small  strips  probably  fill  in  again  by 
vegetative  growth.  Except  where  channels 
are  produced,  drivers  of  small  boats 
generally  avoid  kelp  canopies  as  the  cut 
fronds  easily  foul  propellers  and  water 
intakes  of  engines. 

Various  pipelines,  particularly  from 
offshore  tanker  facilities,  are  placed 
through  kelp  forests.  The  pipe  and  any 
covering  structures,  however,  are  usually 
soon  covered  with  organisms  including 
kelp,  and  probably  have  little  long-term 
impacts.  Short-term  effects  include 
damage  to  organisms  in  the  path  of  the 
pipeline,  and  possible  increased  turbidity 
and  sedimentation  during  construction. 

A  highly  probable  future  use  of  giant 
kelp  forest  habitat  is  for  mariculture 
facilities.  Various  research  programs 
currently  use  kelp  forests  to  test  poten- 
tial culture  techniques,  and  one  lease  has 
been  given  to  grow  Gel idium  robustum  (see 
Plants  above).  Giant  kelp  forests  are 
good  potential  sites  for  abalone  culture. 
With  declining  natural  stocks  and  heavy 
predation  by  man  and  sea  otters  (see  Aba- 
lone  above),  a  profitable  technique  may  be 
to  place  juvenile  abalone  in  structures 
that  encourage  algal  drift  accumulation 

but  discourage  predation,  and  then  place 
these  structures  within  giant  kelp 


6.3.1  Sport  Fishing 

Kelp  forests  are  favored  areas  for 
hook-and-line  and  spear  fishing,  and  sport 
divers  harvest  lobsters,  crabs,  scallops, 
and  abalone  by  hand.  The  extent  of  this 
fishing  and  possible  effects  on  popula- 
tions are  largely  unknown  as  use  and 
catches  are  not  reported.  Miller  and 
Geibel  (1973)  reported  a  540%  increase  in 
sport  diver  activity  from  Pismo  Beach 
(near  San  Luis  Obispo)  to  the  Oregon 
border  between  1960  and  1972.  There  are 
thousands  of  divers  and  sport  fishermen  in 
California,  and  they  are  a  common  sight  in 
kelp  forests  throughout  the  State  when 
weather  conditions  are  favorable.  Numer- 
ous charter  boats  provide  diver  transport 
to  offshore  islands,  especially  Santa 
Catalina  Island  off  Los  Angeles.  Divers 
occasionally  take  non-game  species  as 
curios.  This  is  illegal,  however,  in 
California  without  a  scientific  collecting 

6.3.2  Other  Recreational  Activities 

Numerous  divers  use  giant  kelp  for- 
ests for  underwater  photography  or  simply 
enjoyment,  without  any  fishing.  Non- 
divers  visit  the  coast  to  observe  surface 
organisms  from  shore  or  in  tour  boats;  sea 
otters  are  a  special  attraction  in  central 
Cal ifornia. 

6.3.3  Governmentally  Regulated  Areas 

Many  levels  of  government  have  estab- 
lished a  variety  of  special  use  areas 
along  the  California  coast,  and  some  of 
these  areas  have  been  established  because 
of  their  proximity  to  giant  kelp  forests. 
In  addition  to  city  and  county  parks,  the 
State  has  an  extensive  park  system  where 
fishing,  collecting,  and  other  uses  of 
nearshore  habitats  are  more  highly  regu- 
lated. State  reserves  such  as  the  one  at 
Point  Lobos  near  Carmel  also  regulate 
public  access,  and  in  addition,  further 
restrict  fishing,  collecting,  and  even 
observational  sport  diving.  Miller  and 
Geibel  (1973)  pointed  out  the  value  of 


such  areas  as  natural  baselines  for 
comparisons  with  areas  more  disturbed  by 
man's  activities.  Reserves  also  serve  as 
research  areas  where  study  sites  and 
experiments  are  less  likely  to  be  dis- 
turbed by  man. 

The  Federal  Government  has  recently 
established  the  Channel  Islands  National 
Park  and  National  Marine  Sanctuary  that 
include  Anacapa,  Santa  Cruz,  Santa  Rosa, 
San  Miguel,  and  Santa  Barbara  Islands  off 
southern  California.  The  waters  (includ- 
ing kelp  forests)  in  this  area  have  no 
special  fishing,  collecting,  or  develop- 
ment status  as  a  result  of  the  park,  but 
sanctuary  designation  gives  special  pro- 
tection from  possible  pollution,  including 
new  oil  drilling.  Similar  protection  from 
waste  discharge  is  provided  in  the  34 
coastal  sites  designated  by  the  State 
Water  Resources  Control  Board  as  Areas  of 
Special  Biological  Significance.  Many  of 
these  include  giant  or  bull  kelp  forests 
(e.g.,  Carmel  Bay,  portions  of  Santa 
Catalina  Island,  Saunder's  Reef  near  Point 
Arena) . 


Scientists  use  kelp  forests  for  a 
variety  of  studies,  including  many  that 
provide  background  information  to  aid  in 
management  decisions.  Some  areas,  such  as 
the  Hopkins  Marine  Life  Refuge  at  Point 
Cabrillo  near  Monterey  have  been  estab- 
lished by  the  State  as  scientific  research 
areas.  Unfortunately,  hook-and-line 
fishing  is  often  not  restricted  in  such 
areas,  making  fish  and  fish-related 
studies  difficult.  Scientists  must  have 
collecting  permits  issued  by  the  State  to 
remove  organisms,  and  must  obtain  special 
permission  from  particular  agencies  (e.g., 
park  authorities,  California  Fish  and  Game 
Commission,  refuge  managers)  to  work  in 
parks,  reserves,  and  refuges. 


6.5.1  Pollution  From  Commercial,  Recrea- 
tional, and  Scientific  Use 

The  uses  of  kelp  forests  discussed 
above  generally  do  not  produce  significant 
waste  discharge  or  direct  disturbance  of 
other  organisms.   The  exception  is  the 

introduction  of  the  brown  alga  Sargassum 
muticum  (see  Chapters  3  and  4).  This  alga 
was  accidentally  introduced  into  Washing- 
ton with  oysters  from  Japan.  It  spread 
from  Washington  to  southern  California, 
and  may  displace  giant  kelp  in  some  sites 
at  Santa  Catalina  Island  (Ambrose  and 
Nelson  1982). 

6.5.2  Coastal  and  Inland  Construction 

Coastal  construction  usually  does  not 
directly  impact  offshore  kelp  forests,  but 
it  could  have  indirect  effects  via  changes 
in  water  currents,  turbidity,  and 
sedimentation.  These  effects  have  not 
been  documented  as  they  are  often 
impossible  to  separate  from  natural 
changes  associated  with  varying  oceano- 
graphic  conditions,  storm  intensity,  and 
terrestrial  runoff.  Dams  impede  the  flow 
of  sediment  into  the  ocean.  Their  indi- 
rect effects  have  been  shown  on  beaches, 
but  potential  effects  on  kelp  forests  have 
not  been  studied. 

6.5.3  Oil 

The  effects  of  large  oil  spills  on 
kelp  forest  communities  along  the  western 
Pacific  coast  have  been  studied  twice: 
once  during  the  1957  Tampico  tanker  spill 
in  Baja  California,  Mexico,  and  again 
during  the  1969  Santa  Barbara  offshore 
well  blow-out  and  spill.  The  Tampico 
spill  occurred  when  a  tanker  carrying 
diesel  fuel  wrecked  at  the  mouth  of  a 
small,  shallow  cove  containing  a  small 
stand  of  Macrocystis  pyrifera.  The 
effects  were  studied  by  North  et  al. 
(1964).  Massive  mortality  occurred  among 
invertebrates  (including  sea  urchins, 
abalone,  lobsters,  and  sea  stars).  Damage 
to  plants  was  less  obvious,  and  by  July 

1957,  5  months  after  the  spill,  the 
vegetation  in  the  cove  was  obviously 
increasing  and  juvenile  Macrocystis  were 
abundant.  Algal  species  diversity  and 
abundance  quickly  increased,  with  Macro- 
cystis covering  much  of  the  cove  by  July 

1958.  North  et  al.  (1964)  attributed  the 
increased  algal  growth  to  lack  of  grazing, 
as  most  grazing  animals  were  killed  by  the 
oil.  Most  animals  had  recovered  by  1961, 
but  the  abundances  of  sea  urchins  and 
abalone  had  not  returned  to  pre-spill 
levels  by  1963. 


Crude  oil  from  the  Santa  Barbara 
spill  polluted  a  large  portion  of  the 
mainland  coast,  and  many  of  the  Channel 
Islands  (Foster  et  al.  1971a).  Damage  to 
kelp  forest  communities  is  discussed  in 
Foster  et  al .  (1971b),  and  overall  damage 
to  marine  organisms  is  reviewed  by  Foster 
and  Holmes  (1977).  Assessment  of  spill 
effects  was  complicated  by  record  storms 
that  occurred  at  the  same  time  as  the 
spill.  Numerous  birds  associated  with 
kelp  were  killed  by  the  oil,  but  other 
than  a  decline  in  mysid  shrimp  abundance 
(Ebeling  et  al.  1971),  little  damage  to 
kelp  forest  algae,  invertebrates  or  fishes 
was  observed,  even  though  considerable 
quantities  of  oil  fouled  the  surface 
canopies  (Figure  31).  The  partially 
weathered  crude  oil  appeared  to  stay  on 
the  surface  of  the  water,  and  did  not 
stick  to  the  fronds  of  giant  kelp. 

Additional  damage  may  have  occurred 
if  the  more  volatile  components  of  the  oil 
had  not  had  time  to  evaporate  before 
reaching  shore,  or  if  more  toxic  refined 
products  were  spilled,  as  during  the 
Tampico  wreck.  If  a  spill  like  that  in 
Santa  Barbara  occurred  in  central  Califor- 
nia, it  would  probably  have  a  severe 
impact  on  sea  otters  (see  Section  6.7 
below  and  Siniff  et  al .  1982  for  review). 

Santa  Barbara  and  other  areas  along, 
the  southern  California  coast  have  natural 
oil  seeps  in  or  near  giant  kelp  forests. 
The  oil  from  these  seeps  fouls  beaches  and 
produces  surface  slicks  (Mertz  1959). 
Flow  rates  of  seeps  near  Santa  Barbara 
vary  from  50  to  70  bbl/day  (Allen  et  al. 
1970),  and  oozing  tar  mounds  are  sometimes 
visible  on  the  bottom  within  giant  kelp 
forests  (Spies  and  Davis  1979).  The 
latter  investigators  compared  soft  bottom 
organisms  around  a  subtidal  seep  with 
those  around  non-seep  areas,  and  found  a 
similar  diversity,  but  increased  abun- 
dances near  the  seep.  They  suggested  that 
bacteria  may  degrade  the  oil  and  provide 
an  enriched  food  source  for  the  local 
infauna,  and  that  some  organisms  adapt  to 
oil  exposure  by  producing  enzymes  that 
detoxify  assimilated  oil. 

6.5.4  Power  Plant  Discharge  and  Intake 



The  San  Onofre 
Station  (SONGS)  near 

Nuclear  Generating 
Oceanside  north  of 

Figure  31.  Aerial  photography  of  giant 
kelp  canopy  during  the  Santa  Barbara  oil 
spill.  A,  oil  streaming  from  kelp  canopy; 
B,  black  area  of  heavy  oil  on  beach. 
(Photo  by  Mark  Hurd  Aerial  Surveys, 
Goleta,  Ca. ) 

San  Diego  currently  discharges  heated 
water  in  the  vicinity  of  a  kelp  forest. 
Based  on  a  variety  of  surveys,  the  dis- 
charge from  the  first  operating  unit  of 
this  plant  has  had  little  or  no  effect  on 
the  San  Onofre  kelp  forest  1  km  away 
(McGrath  et  al.  1980).  Two  new  and  larger 
units  recently  began  operation.  These 
have  elaborate  discharge  diffuser  systems 
which  should  eliminate  most  thermal 
effects  (Murdoch  et  al .  1980).  However, 
by  placing  the  intakes  for  these  units  in 
more  turbid,  shallow  water,  and  by  en- 
training large  amounts  of  bottom  water 
during  discharge,  these  units  are 
predicted  to  increase  turbidity  around  the 
discharge  (Murdoch  et  al .  1980).  Because 
the  discharge  pipes  for  these  units  are 
within  200  m  of  the  San  Onofre  kelp 
forest,  the  increased  turbidity  could  have 
significant  impacts  on  Macrocystis  and 


other  plants.  Other  predicted  effects  of 
the  discharge  on  the  kelp  forest  include  a 
reduction  in  nearshore  fish  stocks  due  to 
mortality  of  various  life  stages  during 
intake  and/or  passage  through  SONGS,  a 
reduction  of  mysid  shrimp  in  and  around 
the  kelp  forest  (Murdoch  et  al.  1980),  and 
an  increase  in  fouling  organisms  on  kelp 
blades  (Murdoch  et  al.  1980,  Dixon  et  al. 
1981).  The  kelp  forest  has  been  exten- 
sively studied  by  the  Marine  Review 
Committee  (Murdoch  et  al.  1980),  and 
Southern  California  Edison  Co.  (reviewed 
in  McGrath  et  al.  1980),  and  before-after 
discharge  comparisons  for  the  new  units 
should  provide  comprehensive  information 
on  the  effects  of  the  power  plant  on  the 
kelp  forest  community. 

Another  large  nuclear  power  plant  at 
Diablo  Canyon  near  San  Luis  Obispo  has  not 
yet  gone  into  full  operation.  This  plant 
has  an  intertidal  discharge  that  will 
release  large  volumes  of  heated  water 
directly  into  a  small  cove  with  a  stand  of 
bull  kelp  (Nereocystis  luetkeana) .  Ele- 
vated temperatures  may  eliminate  bull  kelp 
and  other  cold  water  species  in  the  cove, 
and  may  affect  populations  in  the  vicinity 
of  the  cove.  Comprehensive  baseline 
studies  have  been  done  in  the  area  by 
Pacific  Gas  and  Electric  Company  and  the 
California  Department  of  Fish  and  Game,  so 
changes  after  discharge  begins  (assuming 
the  power  plant  starts  operation)  should 
be  well  documented.  It  remains  to  be 
determined  how  (or  if)  biological  changes 
observed  at  these  sites  will  affect  the 
operation  of  the  plants  or  the  siting  and 
operation  of  future  plants. 

Neither  power  plant  is  predicted  to 
cause  significant  changes  in  kelp  forest 
communities  due  to  discharge  of  toxic 
compounds.  Over  1,000  dead  abalone  were 
observed,  however,  in  Diablo  Cove  after  an 
early  cold-water  test  of  the  Diablo  Canyon 
Power  Plant  discharge  system.  Apparently, 
sea  water  was  held  in  the  cooling  system 
for  some  time,  and  then  released.  The  sea 
water  contained  high  levels  of  copper  from 
the  condenser  tubing,  and  when  discharged, 
caused  the  abalone  deaths  (Martin  et  al. 
1977).  Damage  to  other  organisms  was  not 
reported.  The  copper-nickel  tubing  has 
since  been  replaced  by  titanium  (Martin  et 
al.  1977). 

6.5.5  Sewage  Discharge 

Domestic  wastes  contain  nutrients 
that  may  increase  plankton  productivity, 
and  thus  turbidity,  and  may  also  contain 
sludge  particles  that  increase  turbidity 
as  well  as  sedimentation  rates  and  sedi- 
ment thickness  on  the  bottom.  Industrial 
wastes  may  cause  similar  effects,  and  also 
may  contain  toxic  metals  and  organic 
compounds  that  can  directly  affect  organ- 
isms. Discharged  pathogens  may  harm  man 
and  other  organisms.  Thus,  sewage 
discharge  has  the  potential  of  signifi- 
cantly altering  kelp  communities  and  man's 
use  of  them  (Table  1). 

As  discussed  in  Chapters  2  and  3, 
there  is  good  indirect  evidence  that 
sewage  from  the  Los  Angeles  area,  dis- 
charged in  the  vicinity  of  Palos  Verdes, 
contributed  to  the  decline  and  eventual 
complete  loss  of  one  of  the  largest  giant 
kelp  forests  in  California.  The  decline 
of  the  Palos  Verdes  kelp  forest  began  in 
the  1940's  and  1950 '  s  as  discharge  rates 
increased.  The  community  did  not  recover 
after  the  warm  oceanographic  period  of  the 
late  1950's  (Grigg  and  Kiwala  1970,  Wilson 
1982).  Increased  turbidity  (Eppley  et  al. 
1972),  sludge  on  the  bottom  (Grigg  and 
Kiwala  1970),  toxic  substances  in  the 
discharge  such  as  DDT  (Burnett  1971),  and 
possibly  copper  (that  can  inhibit  giant 
kelp  gametophyte  growth  and  fertilization 
at  low  levels;  Smith  1979),  and  other 
metals  may  have  all  contributed  to  the 
decline  and  lack  of  recovery.  With  recent 
improvements  in  discharge  quality,  giant 
kelp  has  begun  to  return  to  the  area 
(Wilson  1982). 

A  similar  but  less  drastic  decline 
occurred  in  the  Point  Loma  kelp  forest, 
one  end  of  which  is  near  discharges  from 
San  Diego,  and  the  other  near  the  entrance 
to  heavily  developed  Mission  Bay.  As  for 
Palos  Verdes,  the  decline  at  Point  Loma 
began  near  the  sewer  discharge  area  (see 
figures  in  North  1976).  Smaller,  primari- 
ly domestic  waste  outfalls  appear  to  have 
quite  localized  effects,  and  no  general 
adverse  impacts  have  been  reported. 



6.6.1  Restoration 

The  declines  in  kelp  forests  around 
sewer  outfalls  and  during  the  warm  water 
years  of  the  late  1950' s  (see  above) 
stimulated  numerous  continuing  attempts  at 
restoration.  The  largest  project  was  the 
Kelp  Habitat  Improvement  Project  under  the 
direction  of  W.  North.  Kelco  Company,  the 
largest  kelp  harvesting  company  in  the 
State  of  California,  has  also  endeavored 
to  increase  Macrocystis  abundance,  parti- 
cularly in  the  Point  Loma  forest  near  San 
Diego.  Most  recent  kelp  restoration 
activities  have  been  by  the  California 
Department  of  Fish  and  Game  (Wilson  and 
McPeak  1983). 

Kelp  restoration  has  variously  in- 
volved killing  sea  urchins,  removing 
possible  competitors  such  as  understory 
kelps,  transplanting  adult  or  juvenile 
Macrocystis,  and  "seeding"  areas  with 
microscopic  sporophytes  grown  in  the 
laboratory  (see  North  1976b  for  a  review). 
Some  or  all  of  these  techniques  have  been 
tried  at  various  times  in  various  areas. 
Sea  urchins  have  been  killed  by  divers 
with  hammers,  by  chemical  treatment  with 
quicklime  (see  Bernstein  and  Welsford  1982 
for  a  description  and  discussion  of  this 
technique),  and  by  causing  animals  to 
aggregate  using  kelp  as  bait  and  then 
removing  them  with  suction  dredges  (Wilson 
and  McPeak  1983).  Quicklime  produces 
lesions  in  sea  urchin  epidermis,  but  also 
causes  damage  to  other  echinoderms  (North 
1963,  1966).  It  is  less  labor  intensive 
than  other  urchin  removal  techniques 
(Wilson  and  McPeak  1983).  As  discussed  in 
Section  2.4  and  elsewhere  in  this  profile, 
dense  stands  of  understory  kelps  such  as 
Pterygophora  californica  can  inhibit  algal 
recruitment,  "so  removal  of  these  plants 
has  also  been  used  to  increase  Macrocystis 
(Wilson  and  McPeak  1983).  All  of  these 
techniques  may  result  in  more  giant  kelp 
in  the  area  manipulated,  if  Macrocystis  is 
nearby  to  provide  a  source  of  spores,  and 
if  environmental  conditions  are  favorable 
for  giant  kelp  recruitment  and  growth. 
Understory  kelps  and  sea  urchins  are 
natural  parts  of  kelp  forest  communities, 
and  one  questions  whether  the  objective  of 

some  of  these  efforts  is  to  restore  the 
natural  giant  kelp  community  or  simply  to 
produce  more  Macrocystis. 

In  areas  where  Macrocystis  is  rare  or 
absent,  adults  and  juveniles  have  been 
transplanted  to  restore  populations.  In 
some  cases,  plants  from  warmer  Mexican 
waters  have  been  used  (North  1972a).  As 
adults  are  large,  transplanting  is  not  an 
easy  task.  Adult  plants  are  pried  from 
the  bottom,  towed  slowly  behind  a  boat  or 
kept  covered  and  wet  on  the  deck,  and  then 
reattached  to  weights  of  various  sorts  at 
the  transplant  site  by  threading  nylon 
rope  though  the  holdfast  and  around  the 
weight  (North  and  Neushul  1968,  North 
1976b).  Juveniles  are  tied  to  suitable 
rocks,  or  to  the  cut  ends  of  Pterygophora 
cal  ifornica  stipes  (North  1976b).  They 
can  also  be  grown  on  plastic  rings  in  the 
laboratory,  and  then  outplanted  (North 
1976b).  If  either  adults  or  juveniles 
remain  healthy,  the  haptera  quickly  grow 
over  the  new  substrata.  The  major  problem 
with  transplanting  large  plants  to  areas 
nearly  devoid  of  vegetation  has  been  fish 
grazing  (see  Section  4.5).  Often,  few  if 
any  plants  survive,  and  transplanting 
enough  to  possibly  exceed  some  minimum 
kelp  biomass  necessary  for  survival  is 
expensive,  and  logistically  difficult. 

Microscopic  sporophytes  can  be  grown 
in  the  laboratory,  and  then  distributed 
over  the  bottom  where  plants  are  desired 
(North  1976b).  This  method  requires  that 
suitable  microsites  be  available  for 
attachment  and  growth,  and  that  other 
environmental  conditions  are  favorable 
(Figure  25).  Because  the  proper  combina- 
tion of  environmental  conditions  necessary 
for  kelp  recruitment,  even  in  the  absence 
of  pollution,  may  occur  infrequently  at  a 
particular  site  (Figure  27),  success  rates 
may  be  low. 

Most  restoration  attempts  using  these 
methods  have  not  had  suitable  controls,  or 
have  not  simultaneously  monitored  vari- 
ables such  as  light  and  temperature,  so 
their  success  is  difficult  to  evaluate. 
Macrocystis  has  returned  to  some  areas 
where  these  techniques  have  been  used, 
particularly  off  Palos  Verdes  near  Los 
Angeles,  and  Point  Loma  near  San  Diego. 
At  Point  Loma,  the  recovery  began  after 
the  sewer  outfall  was  extended  into  deeper 


water,  and  at  Palos  Verdes,  it  began 
coincident  with  a  general  improvement  in 
discharged  water  quality  and  a  large 
increase  in  sea  urchin  fishing  (see  Sewer 
Discharge  above,  and  Wilson  1982).  In 
this  case,  the  significance  of  restoration 
efforts  relative  to  the  other 
environmental  changes  that  may  have 
contributed  to  community  recovery  will 
probably  never  be  known. 

Macrocystis  can  now  be  easily  grown 
from  spore  to  small  juvenile  sporophyte 
(Figure  1)  in  the  laboratory,  so  it  is 
feasible  to  use  these  stages  in  restora- 
tion as  North  (1976b)  has  done  with 
microscopic  sporophytes.  Dean  et  al . 
(1983)  and  Dean  and  Deysher  (1983)  have 
also  used  gametophytes  and  microscopic 
sporophytes  for  large-scale  field  experi- 
ments. In  theory,  the  easiest  method  of 
introducing  kelp  is  to  release  spores  into 
the  area  by  attaching  mesh  bags  with  fer- 
tile sporophylls  to  the  bottom.  Whether 
plants  eventually  result  from  this  pro- 
cedure will  depend  on  a  variety  of  factors 
that  can  affect  the  small  stages  of 
Macrocystis  (Figure  25  and  see  Chapter  5). 

6.6.2  Creating  New  Kelp  Forests 

The  potential  for  producing  large 
amounts  of  fuel  such  as  methane  from  giant 
kelp  (North  1977,  Wise  et  al.  1977),  and 
the  real  or  potential  loss  of  kelp  forests 
as  a  result  of  man's  activities  (such  as 
at  SONGS;  see  Section  6.5.4)  has  stimu- 
lated recent  attempts  to  establish  giant 
kelp  monocultures  or  communities.  An 
initial  effort  to  produce  the  former  was 
tried  offshore  from  southern  California. 
A  structure  with  an  area  of  0.25  acres 
(referred  to  as  the  quarter-acre  module) 
was  moored  in  deep  water,  and  planted  with 
adult  Macrocystis.  Nutrients  were  in- 
creased by  pumping  up  deep  water  (Gerard 
pers.  comm.).  Design  problems,  currents, 
and  even  a  large  sea  urchin  recruitment 
contributed  to  the  failure  of  the  project, 
and  the  structure  was  eventually  lost. 
Neushul  and  Harger  (in  press)  have 
established  a  forest  of  700  adult  plants 
on  a  nearshore  sand  bottom  near  Santa 
Barbara.  Plants  are  anchored  by  putting 
the  holdfasts  in  mesh  bags  filled  with 
gravel  ,  and  the  effects  of  density  and 
fertilization  on  productivity  are  being 
evaluated  (see  Section 

For  fuel  production  to  be  cost 
effective,  Macrocystis  would  have  to  be 
grown  on  a  very  large  scale.  Assuming 
engineering  and  biological  problems  could 
be  solved,  monocultures  of  Macrocystis  or 
other  kelps  covering  many  square  kilo- 
meters of  the  ocean  may  have  significant 
impacts  on  water  quality  and  perhaps  even 
climate,  as  well  as  on  other  uses  of  the 
ocean  such  as  shipping  (Hruby  1978). 
These  issues  remain  to  be  resolved. 

Natural  stand  size  could  be  increased 
in  nearshore  areas  where  present  communi- 
ties are  limited  in  size  only  by  lack  of 
hard  substrata.  This  could  be  done  by 
simply  providing  solid  substrata  such  as 
rock.  This  has  already  been  done  inadver- 
tently in  some  areas  such  as  Goleta  Bay 
near  Santa  Barbara,  where  the  kelp  forest 
has  extended  into  a  shallow  sandy  area. 
In  this  instance,  rock  covering  a  sewage 
discharge  pipeline  that  goes  from  the 
beach  through  the  sand  provided  the 
suitable  substrata  (Foster  pers.  obs.). 
Giant  kelp  forests  have  also  been  created 
in  the  middle  of  large  sandy  areas  by 
placing  rocks  to  form  large  artificial 
reefs  (Davis  et  al.  1982).  In  cases  where 
man's  activities  threaten  or  have  caused 
the  destruction  of  local  kelp  communities, 
such  reefs  are  a  possible  means  of 
compensation  (Grove  1982).  Southern 
California  Edison  Company,  in  conjunction 
with  the  California  Department  of  Fish  and 
Game,  recently  placed  a  reef  (Pendleton 
artificial  reef)  for  this  purpose  near 
Oceanside,  north  of  San  Diego  (Grove  1982, 
Grant  et  al.  1982).  To  date,  over  3  years 
after  construction,  giant  kelp  has  not 
become  established  on  the  reef,  and  adult 
Macrocystis  and  Pterygophora  cal ifornica 
transplanted  to  the  reef  have  been  severe- 
ly damaged  by  fish  grazing  and  storms 
(LOSL  1983).  The  slow  development  has 
probably  also  resulted  from  the  early 
dominance  of  the  substrata  by  particular 
invertebrates  (see  Section, 
precipitous  relief  of  the  reef,  and  the 
relatively  long  distance  from  a  source  of 
spores  and  larvae  (LOSL  1983). 

The  objectives  of  most  prior  artifi- 
cial reefs  and  reef  research  have  been 
fish  attraction  and  fisheries  enhancement, 
and  it  appears  that  the  design  and  place- 
ment of  reefs  for  creating  entire  kelp 
forests  is  a  more  complex  problem.   Based 


on  experience  with  Pendleton  Artificial 
Reef  and  a  review  of  other  reef  and 
various  succession  studies,  timing  of 
placement,  proximity  to  natural  kelp 
stands,  and  physical  relief  appear 
particularly  important  to  rapid  forest 
development  (LOSL  1983).  Reefs  should 
probably  be  "seeded"  with  Macrocystis 
spores  soon  after  placement,  and  may  have 
to  be  further  manipulated  at  various  times 
(e.g.,  remove  grazers,  add  particular 
predators)  if  rapid  community  development 
and  a  persistent  Macrocystis  population 
are  desired  (LOSL  1983).  It  must  also  be 
recognized  that  all  present  and  future 
efforts  to  create  Macrocystis  monocultures 
or  communities  involve  changes  in,  or 
destruction  of,  portions  of  other  communi- 
ties such  as  oceanic  or  sand  bottom. 
Obstructions  on  an  otherwise  level  bottom 
may  also  obstruct  trawls. 

The  first  attempt  to  create  a  "con- 
tained" kelp  forest  is  currently  underway 
in  Monterey,  California.  An  indoor  tank 
9-m  deep  holding  over  1,000,000  liters  of 
sea  water  was  constructed  as  part  of  the 
Monterey  Bay  Aquarium  in  Monterey  (Martin 
pers.  comm.).  This  tank,  with  its  upper 
surface  open  to  the  sky  and  sea  water 
supplied  by  a  large  flow-through  system, 
houses  a  giant  kelp  forest  community  that, 
given  the  tank  size  and  flow  rates,  is 
hoped  to  be  self-sustaining.  For  the 
first  time,  people  are  able  to  view  the 
community  directly  without  diving.  The 
facility  provides  excellent  opportunities 
for  education  and  research. 


The  gray  whale,  brown  pelican,  and 
sea  otter,  all  found  in  and  around  kelp 
forests  (see  Section,  are 
currently  listed  as  threatened  or  endan- 
gered. The  former  two  species  are  common 
in  many  other  habitats,  and  populations  of 
both  are  recovering  now  that  hunting  (in 
the  case  of  the  gray  whale),  and  the  use 
of  DDT  (in  the  case  of  the  brown  pelican) 
have  been  reduced  (see  discussion  in 
Section  They  will  not  be 
discussed  further. 

Sea  otters  are  more  intimately 
associated  with  kelp  forests,  and  their 
management  has  been  more  controversial. 
This  is  partly  because  otter  foraging  has 

significant  impacts  on  particular 
fisheries,  because  sea  otters  are  very 
attractive  to  most  people,  and  because  the 
animal  and  the  fisheries  are  currently 
managed  by  different  agencies.  As  a 
result  of  the  Marine  Mammal  Protection 
Act,  the  U.S.  Fish  and  Wildlife  Service  is 
responsible  for  the  sea  otter,  with  the 
goal  of  developing  optimal  population 
sizes  of  this  animal  consistent  with 
maintenance  of  the  "health"  and  "sta- 
bility" of  the  ecosystem.  The  California 
Department  of  Fish  and  Game  is  also 
responsible  for  the  ecosystem,  organisms 
other  than  mammals,  and  fisheries.  One 
view  of  the  management  problem  is  stated 
by  Hardy  et  al .  (1982):  "If  one  has  a 
legally  mandated  responsibility  to  manage 
shellfish  fisheries  for  maximum  sustain- 
able yield  and  concurrently  manages  a 
shellfish  predator,  the  sea  otter,  for  an 
optimum  sustainable  population,  then 
obviously  a  managerial  dilemma  exists. 
The  superimposition  of  a  higher  managerial 
authority  may  add  further  problems  when 
the  latter' s  prime  concern  is  the 

On  the  fisheries  side  of  the  argu- 
ment, there  is  good  evidence  that  the 
expanding  sea  otter  population  has  elimi- 
nated the  commercial  abalone  fishery 
within  the  otter's  present  range,  and  has 
nearly  eliminated  sport  fisheries  for 
abalone,  Pismo  clams,  and  crabs  (Miller 
and  Geibel  1973,  Stephenson  1977,  Hardy  et 
al.  1982;  but  see  Estes  and  Van  Blaricom 
in  press,  for  alternative  interpreta- 
tions). As  the  population  expands  or  as 
individuals  are  translocated  to  other 
areas,  sea  otters  may  have  further  impacts 
on  these  fisheries  as  well  as  those  for 
lobsters  to  the  south,  and  Dungeness  crabs 
to  the  north.  However,  Van  Blaricom  (in 
press)  points  out  that  sea  otter  foraging 
may  enhance  the  commercial  kelp  harvest, 
and  may  increase  certain  fin-fish  stocks 
and  other  kelp-associated  species.  On  the 
other  side  of  the  argument,  the  sea  otter 
population  in  California  may  still  be 
threatened  with  extinction.  Population 
size  appears  to  have  leveled  off  within 
its  present  range  (see  Section 
There  is  a  debate  over  whether  the 
population  is  at  carrying  capacity  within 
its  present  range,  and  Van  Blaricom  and 
Jameson  (1982)  suggested  that  the  present 
population  could  be  threatened  if  a  large 


oil  spill  occurred.   If  sea  otter  popula-  (1982)  and  in  our  opinion,  this  and  many 

tion  size  and  range  were  to  be  controlled  other  controversies  related  to  sea  otters 

in  some  way  the  techniques  for  contain-  are  discussed  u    in  tne     lar  article 
ment  have  not  been  resolved.   In  addition  ,,„„,»    S 

to   these   problems,   both   management  by   Pleschner   (1984).   The  sea  otter 

agencies   must   contend  with   political  population  is,  at  present,  still  fully 

pressure  from  special-interest  groups.  protected  while  decisions  on  possible 

The  sea  otter-shell  fishery  contro-  translocation   to   other   sites,   zonal 

versy  is  reviewed  in  Cicin-Sain  et  al .  management,  etc.  remain  to  be  made. 




Usually  it  seems  to  be  true  that  when  even  the  most  definitely 
apparent  cause-effect  situations  are  examined  in  the  light  of 
wider  knowledge,  the  cause-effect  aspect  comes  to  be  seen  as 
less  rather  than  more  significant,  and  the  statistical  or  relational 
aspects  acquire  larger  importance.  Steinbeck  (1962). 


Darwin's  (1860)  early  observations 
and  subsequent  studies  by  others  all  agree 
that  giant  kelp  forests  are  exceptional 
biological  entities;  the  abundance  and 
diversity  of  life  associated  with  struc- 
turally complex  and  highly  productive 
Macrocystis  populations  are  obvious  to 
anyone  who  swims  through  one  of  these 
stands  on  a  clear  day.  In  the  preceding 
chapters,  we  described  the  composition, 
distribution,  and  abundance  of  organisms 
in  giant  kelp  forests,  the  factors  that 
affect  community  composition,  what  we 
consider  to  be  lacking  in  our  under- 
standing of  the  ecology  of  these 
communities,  and  necessary  approaches  for 
future  studies. 

Kelp  forest  communities  are  found 
relatively  close  to  shore  along  the  open 
coast,  and  are  influenced  by  local  coastal 
processes  as  well  as  large-scale  oceano- 
graphic  events.  Thus,  a  large  number  of 
factors  can  affect  community  structure  and 
dynamics  at  a  variety  of  spatial  and 
temporal  scales.  Changing  currents  and 
water  masses  affect  temperature,  nutrient 
availability,  and  dispersal  of  spores, 
larvae,  and  adults.  Large-scale 
(geographic)  changes  in  temperature  (and 
perhaps  other  factors;  see  Chapter  5)  and 
the  late  1950' s  and  recent  "El  Nino"  warm- 
water  events  (see  Sections  2.2.3  and 
2.2.5)  are  examples  of  phenomena  that  may 
affect  the  community  over  a  large  area 

(i.e.,  the  entire  range  of  Macrocystis 
pyrifera).  Regional  differences  in 
current  patterns,  exposure  to  swell,  and 
even  degree  of  pollution  due  to  sewage, 
can  affect  the  community  on  a  smaller 
scale  (e.g.,  southern  California).  At  a 
third  level,  very  local  differences  in 
terrestrial  runoff,  substrata,  exposure  to 
swell,  etc.  result  in  great  differences 
among  and  within  stands  over  time. 
Finally,  a  variety  of  abiotic  factors, 
some  of  which  are  influenced  by  the 
organisms  themselves  (e.g.,  shading  by 
Pterygophora  cal ifornica) ,  and  biotic 
factors  affect  distribution  and  abundance 
within  a  particular  stand. 

The  influence  of  large-scale  pheno- 
mena are  most  difficult  to  determine 
because  they  are  difficult  or  impossible 
to  examine  experimentally  (Chapter  5). 
Moreover,  processes  at  all  levels  may 
affect  population  characteristics  on  a 
very  local  scale.  The  current  warm 
oceanographic  period  that  coincided  with 
record  winter  storms  in  1982-83  is  an 
example  of  the  problem.  Numerous  changes 
in  kelp  forests  are  now  commonly  being 
attributed  to  changes  in  water  character- 
istics associated  with  "El  Nino" 
conditions,  but  prior  to  and  during  these 
changes,  associated  storms  drastically 
reduced  Macrocystis  abundance  in 
California.  Therefore,  without  site- 
specific  demographic  studies,  the  relative 
importance  of  these  events  to  the  present 


condition  of  particular  forests  will 
probably  be  confused,  and  correlations 
with  one  event  or  the  other  could  be 
misleading.  Good  descriptive  studies  at  a 
variety  of  sites,  combined  with  experi- 
mental tests  of  hypotheses  and  demographic 
analyses  that  include  monitoring  of 
environmental  variables,  appear  most 
appropriate  for  unravelling  the  complexi- 
ties of  kelp  forest  ecology.  However, 
even  this  approach  can  be  confounded  by 
historical  events,  making  the  interpre- 
tation of  present  patterns  difficult 
(Dayton  and  Tegner  1984a). 

Listed  below  are  generalizations 
about  the  ecology  of  giant  kelp  forests 
that  have  emerged  from  our  review  of  the 
literature,  along  with  suggestions  for 
future  studies.  For  reasons  discussed  at 
length  in  Chapter  5,  these  generalizations 
should  be  considered  working  hypotheses. 
They  are  made  in  the  context  of  within  the 
geographic  range  of  Macrocystis  pyrifera 
and  within  the  limits  of  temperature, 
salinity,  nutrients,  and  light  necessary 
for  giant  kelp  to  persist.  They  apply  to 
the  entire  life  histories  of  the  species 

1.  The  primary  requirement  for  the 
existence  of  a  kelp  forest  is  hard  sub- 
strata (Chapter  2).  Lack  of  hard 
substrata  commonly  accounts  for  the 
absence  of  the  community  within  depths, 
and  often  determines  the  deeper,  offshore 
boundary  of  the  community.  More  studies 
are  needed  on  the  effects  of  sedimentation 
and  burial  on  community  structure  and 

2.  Extreme  water  motion  associated 
with  storms  is  very  important  to  community 
structure  in  central  California,  and 
occasionally  important  in  southern 
California  (Chapters  2  and  3).  Storms 
commonly  remove  canopies  and  entire 
plants,  can  directly  or  indirectly  lead  to 
the  invasion  and  proliferation  of  species 
other  than  Macrocystis ,  and  may  determine 
the  shallow,  inshore  boundary  of  giant 
kelp  distribution.  Water  motion  also  has 
important  effects  on  the  abundance  and 
behavior  of  other  species.  Studies  are 
needed  to  determine  the  relationship  of 
holdfast  structure,  frond  abundance,  and 
frond  size  to  mortality  of  Macrocystis 
during  periods  of  extreme  water  motion. 

3.  Local  differences  in  light, 
caused  by  changes  in  abiotic  conditions 
and,  more  especially,  by  various  canopy 
layers,  have  a  profound  effect  on  algal 
growth  and  recruitment  and  probably  the 
deeper,  offshore  boundary  of  giant  kelp 
distribution  (Chapters  2  and  3).  Coordi- 
nated laboratory  and  field  studies  of  the 
light  requirements  for  species  other  than 
Macrocysitis  are  needed,  as  are  studies  of 
the  relationship  between  variations  in 
light  characteristics  and  the  distribution 
of  plant  species  within  a  kelp  forest. 

4.  Variability  in  temperature  and 
nutrients  affects  community  structure, 
particularly  in  southern  California 
(Chapter  2).  The  effects  of  these  abiotic 
factors  on  organisms  other  than  Macro- 
cystis need  further  study. 

5.  Spore  and  larval  dispersal  are 
important  to  population  and  community 
structure  (Chapters  3,  4  and  5).  Studies 
of  dispersal  and  its  effects  on  community 
structure  and  dynamics  are  few  and 
difficult  to  do,  but  essential  to  our 
understanding  of  kelp  forest  ecology. 

6.  Some  grazers,  particularly  sea 
urchins,  have  large,  local  effects  on  the 
community  by  removing  algae  and  preventing 
recruitment  (Chapters  3  and  4).  Grazers 
may  alter  species  assemblages,  allowing 
invasion  and  dominance  of  species  differ- 
ent from  those  consumed.  More  information 
is  needed  on  the  distribution  and  abun- 
dance of  sea  urchins  within  areas  and 
among  broader  areas  of  coastline  to 
provide  a  context  for  their  effects. 
Information  is  also  needed  on  the  effects 
of  grazers  other  than  sea  urchins  (e.g., 
small  crustaceans,  Patiria  miniata). 

7.  Sea  otters  cause  reductions  in 
invertebrate  densities,  particularly  those 
of  sea  urchins  and  abalone  (Chapters  4  and 
5);  reductions  in  the  numbers  of  sea 
urchins  can  cause  an  increase  in  kelp  and 
other  foliose  algae.  The  spatial  scale  of 
these  increases  will  vary  depending  on  the 
distribution,  abundance,  and  behavior  of 
sea  urchins  prior  to  their  reduction.  The 
relationship  between  sea  otter  foraging  in 
California  and  the  "health"  and  "stabil- 
ity" of  kelp  communities  needs  to  be 
examined  in  both  the  general  and  local 
contexts  of  grazer  effects  without  otters, 


the  effects  of  other  urchin  predators,  and 
the  influence  of  man  (aboriginal  and 

8.  Man  may  have  had  a  profound 
impact  on  kelp  forests  through  the 
historical  hunting  of  mammals,  and  has  had 
a  recent  impact  by  discharging  wastes  in 
southern  California  (Chapters  4  and  6). 

The  above  generalizations  are  a 
subset  of  the  factors  listed  in  Table  1, 
and  cover  a  subset  of  possible  scales  of 
effects  outlined  in  Figure  26;  their 
relative  importance  varies  locally  and  on 
different  spatial  and  temporal  scales. 
This  suggests  that  single  factors  and 
simple  cause-effect  relationships  will 
never  explain  or  predict  kelp  forest 
community  structure.  What  seems  probable 
are  typologies  where  the  relative  influ- 
ence of  various  factors  are  assigned  to 
different  "types"  of  forests  at  different 
spatial  and  temporal  scales.  Thus,  water 
motion  may  be  most  important  to  the 
structure  of  giant  kelp  communities 
growing  on  relatively  soft  rock  and 
exposed  to  extreme  water  motion  (e.g., 
Sandhill  Bluff,  Section  3.3.1  and  Figure 
5).  Sites  under  these  conditions  may  form 
one  site  type.  Dispersal  and  light 
reduction  may  be  important  on  the  scale  of 
meters,  but  not  tens  of  meters,  to  the 
ecology  of  stands  of  understory  kelps. 
Extreme  water  motion  is  important  on  the 
scale  of  tens  of  years  but  not  years. 

Such  a  classification  scheme, 
emphasizing  the  relationships  between 
sites,  scales  and  factors,  is  similar  to 
that  in  an  analysis  of  variance,  and  would 
help  remove  some  of  the  confusion  that 
results  from  mixing  different  scales  and 
from  generalizing  about  "kelp  forests" 
from  one  "kelp  forest."  It  would  also 
provide  a  more  rigorous  context  for  future 
investigations  (for  a  general  discussion 
of  this  kind  of  organization  see  Bateson 
1972,  pages  279-308,  and  1979,  Chapter  7). 
More  thorough  descriptive  studies  at  a 
variety  of  different  sites  and  spatial 
scales  are  needed  for  development  of  such 
a  system,  but  it  may  be  worthwhile  to 
attempt  a  tentative  classification  based 
on  our  present  information. 

There  appear  to  be  three  main  dif- 
ferences between  temperate  subtidal  reefs 

with  and  without  Macrocystis:  giant  kelp 
increases  three-dimensional  structure  by 
providing  living  microhabitats  such  as 
holdfasts  and  surface  canopy  that  are 
reduced  or  unavailable  where  giant  kelp  is 
absent.  Macrocystis  also  provides 
increased  productivity  and,  thirdly,  the 
majority  of  this  production  is  used  as 
detritus  (Chapters  3  and  4). 

The  quantities  of  drift  kelp,  both 
within  kelp  forests  and  in  other  communi- 
ties such  as  sandy  beaches,  and  the  high 
abundances  and  diversity  of  organisms 
within  forests  that  can  use  this  drift  and 
detrital  material  (perhaps  directly  with 
little  or  no  prior  degradation  and  energy 
loss  through  microbial  decomposition),  all 
suggest  that  Macrocystis  stimulates  the 
development  of  food  webs  based  on  detritus 
(Chapter  3).  Further  studies  of  the 
effects  of  habitats  created  by  Macrocystis 
on  the  remainder  of  the  community,  and  of 
differences  in  detritus  versus  plankton 
feeding  among  assemblages  in  areas  with 
and  without  giant  kelp,  may  thus  reveal 
important  structural  and  functional 
differences  between  Macrocystis  and  other 
nearshore  reef  communities. 


Management  of  kelp  forests  is 
hampered  by  site-specific  community 
differences,  lack  of  information  about  the 
causes  of  these  differences,  conflicting 
uses  of  the  community,  and  pressures  from 
special-interest  groups  (Chapter  6).  Even 
if  the  latter  three  problems  are  solved, 
it  is  clear  that  evaluations  of  the 
effects  of  proposed  activities  such  as  new 
sewer  outfalls  will  still  have  to  be  based 
on  local  studies  of  the  particular  forest 
likely  to  be  impacted  (Foster  et  al. 
1983).  Even  with  thorough  studies, 
uncertainties  about  effects  will  remain. 

Kelp  forests  have  recovered  where  the 
quality  of  discharged  sewage  has  improved, 
or  when  the  locations  of  outfalls  have 
been  changed  (Section  6.5.5).  It  is  also 
true  that  many  direct  and  probably 
indirect  changes  in  kelp  forest  popula- 
tions are  caused  by  overfishing  (Section 
6.6.2).  On  the  other  hand,  although  kelp 
forest  restoration  attempts  are  still  in 
the  research  phase,  it  appears  that  this 
form  of  management  is,  and  will  continue 


to  be,  extremely  labor  and  time  intensive, 
and  may  be  impossible  to  implement  on  a 
large  scale.  This  all  suggests  that  the 
most  effective  management  is  preventing 
degradation  rather  than  attempting  local 
cures  after  degradation  has  occurred. 
Thus,  management  via  more  stringent  water 
quality  standards  for  existing  and  future 
ocean  discharges  of  all  sorts,  and  via 
fishing  regulations  that  do  not  allow 
drastic  population  reductions  before 
significant  regulation  occurs,  is  most 
appropriate  and  probably  essential  to 
natural  restoration  and  the  prevention  of 
future  resource  losses. 

rank  various  basic  and  applied  research 
areas.  Basic  population  studies  (recruit- 
ment, growth,  mortality,  reproduction)  of 
"important"  kelp  forest  organisms,  studies 
of  physical  processes  that  structure  kelp 
ecosystems,  and  the  functional  role  of 
biological  processes  such  as  competition 
and  predation  received  the  highest 
rankings  for  basic  research.  Studies  of 
the  biological  and  socio-economic  con- 
sequences of  possible  sea  otter  management 
alternatives,  multi-species  approaches  to 
biological  and  economic  modeling,  and 
stock  enhancement  received  the  highest 
ranking   among  applied  research  needs. 


We  have  recommended  needed  research 
in  a  number  of  places  in  the  profile, 
particularly  in  Chapter  5  and  in  the 
generalizations  above.  These  suggestions 
are  generally  in  accord  with  those  of 
others  who  work  in  kelp  forests.  At  a 
1979  meeting  of  kelp  forest  biologists 
(Anon  1979),  participants  were  asked  to 

Research  needs  will  change,  but  these 
suggested  studies,  done  and  interpreted  in 
the  context  of  site  types  and  spatial  and 
temporal  scales  outlined  above,  would 
certainly  improve  our  understanding  of 
kelp  forest  communities  and  help  solve 
some  of  the  problems  associated  with  man's 
use  of  them. 




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Point  Reyes  Bird  Observatory 

Stinson  Beach,  CA  94970 

Baldridge,  A. 

Hopkins  Marine  Station  of  Stanford 

Pacific  Grove,  CA  93950 


Barilotti,  D.C. 
Kelco  Company 
P.O.  Box  13216 
San  Diego,  CA  92113 

Bonnell ,  M.  L. 

Center  for  Coastal  Marine  Studies 

University  of  California 

Santa  Cruz,  CA  95064 

Carr,  M. 

Department  of  Bi logical  Sciences 
University  of  California 
Santa  Barbara,  CA  93106 

Carter,  J. 

Kinnetic  Labs 

5365  Avenida  Encinitas,  Suite  H 

Carlsbad,  CA  92008 

Cowen,  R. 

Scripps  Institution  of 

Oceanography,  A-008 
La  Jolla,  CA  92093 

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Moss  Landing  Marine  Laboratories 

P.O.  Box  450 

Moss  Landing,  CA  95039-0450 

Dean,  T.A. 

Kelp  Ecology  Project 

531  Encinitas  Blvd. ,  Suite  118 

Encinitas,  CA  92024 

Deysher,  L. 

Kelp  Ecology  Project 

531  Encinitas  Blvd.,  Suite  118 

Encinitas,  CA  92024 

Dixon,  J. 

Kelp  Invertebrate  Project 
531  Encinitas  Blvd. ,  Suite 
Encinitas,  CA  92024 


Druehl ,  L. 

Department  of  Bilogical  Sciences 

Simon  Fraser  University 

Burnaby  2,  British  Columbia 


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California  Department  of 
Granite  Canyon  Mariculture 
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Estes,  J. 


Center  for  Coastal  Marine  Studies 

University  of  California 

Santa  Cruz,  CA  95064 

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Marine  Sciences  Research  Center 
State  University  of  New  York 
Stony  Brook,  NY  11794 

Harrold,  C. 

Center  for  Coastal  Marine  Studies 

University  of  California 

Santa  Cruz,  CA  95064 

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Piedras  Blancas  Field  Station 

P.O.  Box  67 

San  Simeon,  CA  93452-0067 

Keating,  T. 

Moss  Landing  Marine  Laboratories 

P.O.  Box  450 

Moss  Landing,  CA  95039-0450 

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Department  of  Zoology 
University  of  Sydney 
Sydney,  N.S.W.  2006 
Austral ia 

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Tera  Corp. 

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Avila  Beach,  CA  93424-400 

Laur,  D. 

Department  of  Biological  Sciences 

University  of  California 

Santa  Barbara,  CA  93106 

Martin,  L. 

Monterey  Bay  Aquarium 

Monterey,  CA  93940 

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Kelco  Company 

P.O.  Box  13216 

San  Diego,  CA  92113-13216 

Miller,  D.J. 

c/o  California  Department  of  Fish  and  Game 

2201  Garden  Road 

Monterey,  CA  93940 


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California  Institute  of  Technology 
W.M.  Keck  Engineering  Laboratories 
Pasadena,  CA  92125 

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Center  for  Coastal  Marine  Studies 

University  of  California 

Santa  Cruz,  CA  95064 

Reed,  D. 

Department  of  Biological  Sciences 

University  of  California 

Santa  Barbara,  CA  93106 

Schroeter,  S. 
Kelp  Invertebrate  Project 
531  Encinitas  Blvd. ,  Suite 
Encinitas,  CA  92024 


Van  Blaricom,  G. 


Center  for  Coastal  Marine  Studies 

University  of  California 

Santa  Cruz,  CA  95064 

Zimmerman,  R. 

Department  of  Biological  Sciences 
University  of  Southern  California 
Los  Angeles,  CA  90089 


5027;  -1Q1 


1.    REPORT    NO. 

Biological   Report  85(7.2) 

I  2- 

3.    Recipient's   Accession    No 

4.    Title    and    Subtitle 

The  Ecology  of  Giant  Kelp  Forests  in  California:  A  Community 

5.    Report    Date 

May  1985 

7.   Author(s) 

Michael  S.  Foster  and  David  R.  Schiel 

S.    Pertorming  Organization   Rept    No 

9.    Performing    Organization    Name    and   Address 

10.    Proiecf /TasWWork   Unit   No 

Moss  Landing  Marine  Laboratories 

P.O.  Box  450 

Moss  Landing,  California  95039-0450 

11.    Conlracl(C)  or  Grant(G)   No. 



12.    Sponsoring  Organization  Name  and  Address 

National  Coastal  Ecosystems  Team 
Fish  and  Wildlife  Service 
Division  of  Biological  Services 
Washington,  DC  20240 

13.    Type  of  Report    &   Period   Covered 

15.    Supplementary   Notes 

IS.    Abstract    (Limit:    200  words) 

Giant  kelp  forests  are  marine  communities  dominated  by  the  large  brown  alga, 
Macrocystis  pyrifera.  In  the  northern  hemisphere,  stands  of  this  species  occur 
along  the  outer  coast  of  the  eastern  Pacific  from  near  Santa  Cruz  in  central 
California  to  the  central  coast  of  Baja  California,  Mexico.  Plants  are  usually 
attached  to  rocky  substrata  at  depths  of  5-20  m.  These  submarine  forests  are 
probably  the  most  species-rich,  structurally  complex  and  productive  communities  in 
temperate  waters. 

This  profile  reviews  the  relevant  literature  (over  400  citations)  describing 
M.  pyrifera,  the  organisms  associated  with  it,  the  interactions  among  these 
organisms,  and  environmental  factors  that  affect  the  distribution  and  structure  of 
the  community.  The  state  of  our  knowledge  about  giant  kelp  forests  is  summarized, 
and  suggestions  are  made  for  future  research  and  management. 

17.    Document  Analysis      a.    Descriptors 

Giant  kelp,  Macrocystis  pyrifera,  Distribution,  Abundance,  Hypotheses,  Review,  Community 
Structure,  Understory  Algae,  Invertebrates,  Fish,  Birds,  Mammals,  Resource  Use,  Management 

b.    Identifiers/Open  Ended    Terms 

Kelp  Forests,  California,  Baja  California,  Subtidal  Community,  Ecology,  Marine 

c.    COSATI    Field/Group 

18.    Availability    Statement 


19.    Security   Class   (This    Report) 


20.    Security  Class  (This  Page) 


21.    No    of   Pages 


(See  ANSI-Z39  18) 

*U.S.    GOVERNMENT    PRINTING    OFFICE:       1985—    573-282 

OPTIONAL  FORM    272  (4-77) 
(Formerly   NTIS-3S) 
Department  of  Commerce 

-&    Headquarters.  Division  of  Biological 
Services,  Washington,  DC 

x     Eastern  Energy  and  Land  Use  Team 
Leetown,  WV 

*  National  Coastal  Ecosystems  Team 

Slidell.  LA 

0     Western  Energy  and  Land  Use  Teai 
Ft    Collins,  CO 

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sibility for  most  of  our  nationally  owned  public  lands  and  natural  resources.  This  includes 
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